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7	Network Working Group P. Resnick, Ed.
8	Request for Comments: 5322 Qualcomm Incorporated
9	Obsoletes: 2822 October 2008
10	Updates: 4021
11	Category: Standards Track
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14	Internet Message Format
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16	Status of This Memo
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18	This document specifies an Internet standards track protocol for the
19	Internet community, and requests discussion and suggestions for
20	improvements. Please refer to the current edition of the "Internet
21	Official Protocol Standards" (STD 1) for the standardization state
22	and status of this protocol. Distribution of this memo is unlimited.
23
24	Abstract
25
26	This document specifies the Internet Message Format (IMF), a syntax
27	for text messages that are sent between computer users, within the
28	framework of "electronic mail" messages. This specification is a
29	revision of Request For Comments (RFC) 2822, which itself superseded
30	Request For Comments (RFC) 822, "Standard for the Format of ARPA
31	Internet Text Messages", updating it to reflect current practice and
32	incorporating incremental changes that were specified in other RFCs.
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58	Resnick Standards Track [Page 1]
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60	RFC 5322 Internet Message Format October 2008
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62
63	Table of Contents
64
65	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
66	1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4
67	1.2. Notational Conventions . . . . . . . . . . . . . . . . . . 5
68	1.2.1. Requirements Notation . . . . . . . . . . . . . . . . 5
69	1.2.2. Syntactic Notation . . . . . . . . . . . . . . . . . . 5
70	1.2.3. Structure of This Document . . . . . . . . . . . . . . 5
71	2. Lexical Analysis of Messages . . . . . . . . . . . . . . . . . 6
72	2.1. General Description . . . . . . . . . . . . . . . . . . . 6
73	2.1.1. Line Length Limits . . . . . . . . . . . . . . . . . . 7
74	2.2. Header Fields . . . . . . . . . . . . . . . . . . . . . . 8
75	2.2.1. Unstructured Header Field Bodies . . . . . . . . . . . 8
76	2.2.2. Structured Header Field Bodies . . . . . . . . . . . . 8
77	2.2.3. Long Header Fields . . . . . . . . . . . . . . . . . . 8
78	2.3. Body . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
79	3. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
80	3.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 10
81	3.2. Lexical Tokens . . . . . . . . . . . . . . . . . . . . . . 10
82	3.2.1. Quoted characters . . . . . . . . . . . . . . . . . . 10
83	3.2.2. Folding White Space and Comments . . . . . . . . . . . 11
84	3.2.3. Atom . . . . . . . . . . . . . . . . . . . . . . . . . 12
85	3.2.4. Quoted Strings . . . . . . . . . . . . . . . . . . . . 13
86	3.2.5. Miscellaneous Tokens . . . . . . . . . . . . . . . . . 14
87	3.3. Date and Time Specification . . . . . . . . . . . . . . . 14
88	3.4. Address Specification . . . . . . . . . . . . . . . . . . 16
89	3.4.1. Addr-Spec Specification . . . . . . . . . . . . . . . 17
90	3.5. Overall Message Syntax . . . . . . . . . . . . . . . . . . 18
91	3.6. Field Definitions . . . . . . . . . . . . . . . . . . . . 19
92	3.6.1. The Origination Date Field . . . . . . . . . . . . . . 22
93	3.6.2. Originator Fields . . . . . . . . . . . . . . . . . . 22
94	3.6.3. Destination Address Fields . . . . . . . . . . . . . . 23
95	3.6.4. Identification Fields . . . . . . . . . . . . . . . . 25
96	3.6.5. Informational Fields . . . . . . . . . . . . . . . . . 27
97	3.6.6. Resent Fields . . . . . . . . . . . . . . . . . . . . 28
98	3.6.7. Trace Fields . . . . . . . . . . . . . . . . . . . . . 30
99	3.6.8. Optional Fields . . . . . . . . . . . . . . . . . . . 30
100	4. Obsolete Syntax . . . . . . . . . . . . . . . . . . . . . . . 31
101	4.1. Miscellaneous Obsolete Tokens . . . . . . . . . . . . . . 32
102	4.2. Obsolete Folding White Space . . . . . . . . . . . . . . . 33
103	4.3. Obsolete Date and Time . . . . . . . . . . . . . . . . . . 33
104	4.4. Obsolete Addressing . . . . . . . . . . . . . . . . . . . 35
105	4.5. Obsolete Header Fields . . . . . . . . . . . . . . . . . . 35
106	4.5.1. Obsolete Origination Date Field . . . . . . . . . . . 36
107	4.5.2. Obsolete Originator Fields . . . . . . . . . . . . . . 36
108	4.5.3. Obsolete Destination Address Fields . . . . . . . . . 37
109	4.5.4. Obsolete Identification Fields . . . . . . . . . . . . 37
110	4.5.5. Obsolete Informational Fields . . . . . . . . . . . . 37
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119	4.5.6. Obsolete Resent Fields . . . . . . . . . . . . . . . . 38
120	4.5.7. Obsolete Trace Fields . . . . . . . . . . . . . . . . 38
121	4.5.8. Obsolete optional fields . . . . . . . . . . . . . . . 38
122	5. Security Considerations . . . . . . . . . . . . . . . . . . . 38
123	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39
124	Appendix A. Example Messages . . . . . . . . . . . . . . . . . 43
125	Appendix A.1. Addressing Examples . . . . . . . . . . . . . . . 44
126	Appendix A.1.1. A Message from One Person to Another with
127	Simple Addressing . . . . . . . . . . . . . . . . 44
128	Appendix A.1.2. Different Types of Mailboxes . . . . . . . . . . . 45
129	Appendix A.1.3. Group Addresses . . . . . . . . . . . . . . . . . 45
130	Appendix A.2. Reply Messages . . . . . . . . . . . . . . . . . . 46
131	Appendix A.3. Resent Messages . . . . . . . . . . . . . . . . . 47
132	Appendix A.4. Messages with Trace Fields . . . . . . . . . . . . 48
133	Appendix A.5. White Space, Comments, and Other Oddities . . . . 49
134	Appendix A.6. Obsoleted Forms . . . . . . . . . . . . . . . . . 50
135	Appendix A.6.1. Obsolete Addressing . . . . . . . . . . . . . . . 50
136	Appendix A.6.2. Obsolete Dates . . . . . . . . . . . . . . . . . . 50
137	Appendix A.6.3. Obsolete White Space and Comments . . . . . . . . 51
138	Appendix B. Differences from Earlier Specifications . . . . . 52
139	Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . 53
140	7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 55
141	7.1. Normative References . . . . . . . . . . . . . . . . . . . 55
142	7.2. Informative References . . . . . . . . . . . . . . . . . . 55
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174
175	1. Introduction
176
177	1.1. Scope
178
179	This document specifies the Internet Message Format (IMF), a syntax
180	for text messages that are sent between computer users, within the
181	framework of "electronic mail" messages. This specification is an
182	update to [RFC2822], which itself superseded [RFC0822], updating it
183	to reflect current practice and incorporating incremental changes
184	that were specified in other RFCs such as [RFC1123].
185
186	This document specifies a syntax only for text messages. In
187	particular, it makes no provision for the transmission of images,
188	audio, or other sorts of structured data in electronic mail messages.
189	There are several extensions published, such as the MIME document
190	series ([RFC2045], [RFC2046], [RFC2049]), which describe mechanisms
191	for the transmission of such data through electronic mail, either by
192	extending the syntax provided here or by structuring such messages to
193	conform to this syntax. Those mechanisms are outside of the scope of
194	this specification.
195
196	In the context of electronic mail, messages are viewed as having an
197	envelope and contents. The envelope contains whatever information is
198	needed to accomplish transmission and delivery. (See [RFC5321] for a
199	discussion of the envelope.) The contents comprise the object to be
200	delivered to the recipient. This specification applies only to the
201	format and some of the semantics of message contents. It contains no
202	specification of the information in the envelope.
203
204	However, some message systems may use information from the contents
205	to create the envelope. It is intended that this specification
206	facilitate the acquisition of such information by programs.
207
208	This specification is intended as a definition of what message
209	content format is to be passed between systems. Though some message
210	systems locally store messages in this format (which eliminates the
211	need for translation between formats) and others use formats that
212	differ from the one specified in this specification, local storage is
213	outside of the scope of this specification.
214
215	Note: This specification is not intended to dictate the internal
216	formats used by sites, the specific message system features that
217	they are expected to support, or any of the characteristics of
218	user interface programs that create or read messages. In
219	addition, this document does not specify an encoding of the
220	characters for either transport or storage; that is, it does not
221	specify the number of bits used or how those bits are specifically
222	transferred over the wire or stored on disk.
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230
231	1.2. Notational Conventions
232
233	1.2.1. Requirements Notation
234
235	This document occasionally uses terms that appear in capital letters.
236	When the terms "MUST", "SHOULD", "RECOMMENDED", "MUST NOT", "SHOULD
237	NOT", and "MAY" appear capitalized, they are being used to indicate
238	particular requirements of this specification. A discussion of the
239	meanings of these terms appears in [RFC2119].
240
241	1.2.2. Syntactic Notation
242
243	This specification uses the Augmented Backus-Naur Form (ABNF)
244	[RFC5234] notation for the formal definitions of the syntax of
245	messages. Characters will be specified either by a decimal value
246	(e.g., the value %d65 for uppercase A and %d97 for lowercase A) or by
247	a case-insensitive literal value enclosed in quotation marks (e.g.,
248	"A" for either uppercase or lowercase A).
249
250	1.2.3. Structure of This Document
251
252	This document is divided into several sections.
253
254	This section, section 1, is a short introduction to the document.
255
256	Section 2 lays out the general description of a message and its
257	constituent parts. This is an overview to help the reader understand
258	some of the general principles used in the later portions of this
259	document. Any examples in this section MUST NOT be taken as
260	specification of the formal syntax of any part of a message.
261
262	Section 3 specifies formal ABNF rules for the structure of each part
263	of a message (the syntax) and describes the relationship between
264	those parts and their meaning in the context of a message (the
265	semantics). That is, it lays out the actual rules for the structure
266	of each part of a message (the syntax) as well as a description of
267	the parts and instructions for their interpretation (the semantics).
268	This includes analysis of the syntax and semantics of subparts of
269	messages that have specific structure. The syntax included in
270	section 3 represents messages as they MUST be created. There are
271	also notes in section 3 to indicate if any of the options specified
272	in the syntax SHOULD be used over any of the others.
273
274	Both sections 2 and 3 describe messages that are legal to generate
275	for purposes of this specification.
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286
287	Section 4 of this document specifies an "obsolete" syntax. There are
288	references in section 3 to these obsolete syntactic elements. The
289	rules of the obsolete syntax are elements that have appeared in
290	earlier versions of this specification or have previously been widely
291	used in Internet messages. As such, these elements MUST be
292	interpreted by parsers of messages in order to be conformant to this
293	specification. However, since items in this syntax have been
294	determined to be non-interoperable or to cause significant problems
295	for recipients of messages, they MUST NOT be generated by creators of
296	conformant messages.
297
298	Section 5 details security considerations to take into account when
299	implementing this specification.
300
301	Appendix A lists examples of different sorts of messages. These
302	examples are not exhaustive of the types of messages that appear on
303	the Internet, but give a broad overview of certain syntactic forms.
304
305	Appendix B lists the differences between this specification and
306	earlier specifications for Internet messages.
307
308	Appendix C contains acknowledgements.
309
310	2. Lexical Analysis of Messages
311
312	2.1. General Description
313
314	At the most basic level, a message is a series of characters. A
315	message that is conformant with this specification is composed of
316	characters with values in the range of 1 through 127 and interpreted
317	as US-ASCII [ANSI.X3-4.1986] characters. For brevity, this document
318	sometimes refers to this range of characters as simply "US-ASCII
319	characters".
320
321	Note: This document specifies that messages are made up of
322	characters in the US-ASCII range of 1 through 127. There are
323	other documents, specifically the MIME document series ([RFC2045],
324	[RFC2046], [RFC2047], [RFC2049], [RFC4288], [RFC4289]), that
325	extend this specification to allow for values outside of that
326	range. Discussion of those mechanisms is not within the scope of
327	this specification.
328
329	Messages are divided into lines of characters. A line is a series of
330	characters that is delimited with the two characters carriage-return
331	and line-feed; that is, the carriage return (CR) character (ASCII
332	value 13) followed immediately by the line feed (LF) character (ASCII
333	value 10). (The carriage return/line feed pair is usually written in
334	this document as "CRLF".)
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342
343	A message consists of header fields (collectively called "the header
344	section of the message") followed, optionally, by a body. The header
345	section is a sequence of lines of characters with special syntax as
346	defined in this specification. The body is simply a sequence of
347	characters that follows the header section and is separated from the
348	header section by an empty line (i.e., a line with nothing preceding
349	the CRLF).
350
351	Note: Common parlance and earlier versions of this specification
352	use the term "header" to either refer to the entire header section
353	or to refer to an individual header field. To avoid ambiguity,
354	this document does not use the terms "header" or "headers" in
355	isolation, but instead always uses "header field" to refer to the
356	individual field and "header section" to refer to the entire
357	collection.
358
359	2.1.1. Line Length Limits
360
361	There are two limits that this specification places on the number of
362	characters in a line. Each line of characters MUST be no more than
363	998 characters, and SHOULD be no more than 78 characters, excluding
364	the CRLF.
365
366	The 998 character limit is due to limitations in many implementations
367	that send, receive, or store IMF messages which simply cannot handle
368	more than 998 characters on a line. Receiving implementations would
369	do well to handle an arbitrarily large number of characters in a line
370	for robustness sake. However, there are so many implementations that
371	(in compliance with the transport requirements of [RFC5321]) do not
372	accept messages containing more than 1000 characters including the CR
373	and LF per line, it is important for implementations not to create
374	such messages.
375
376	The more conservative 78 character recommendation is to accommodate
377	the many implementations of user interfaces that display these
378	messages which may truncate, or disastrously wrap, the display of
379	more than 78 characters per line, in spite of the fact that such
380	implementations are non-conformant to the intent of this
381	specification (and that of [RFC5321] if they actually cause
382	information to be lost). Again, even though this limitation is put
383	on messages, it is incumbent upon implementations that display
384	messages to handle an arbitrarily large number of characters in a
385	line (certainly at least up to the 998 character limit) for the sake
386	of robustness.
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398
399	2.2. Header Fields
400
401	Header fields are lines beginning with a field name, followed by a
402	colon (":"), followed by a field body, and terminated by CRLF. A
403	field name MUST be composed of printable US-ASCII characters (i.e.,
404	characters that have values between 33 and 126, inclusive), except
405	colon. A field body may be composed of printable US-ASCII characters
406	as well as the space (SP, ASCII value 32) and horizontal tab (HTAB,
407	ASCII value 9) characters (together known as the white space
408	characters, WSP). A field body MUST NOT include CR and LF except
409	when used in "folding" and "unfolding", as described in section
410	2.2.3. All field bodies MUST conform to the syntax described in
411	sections 3 and 4 of this specification.
412
413	2.2.1. Unstructured Header Field Bodies
414
415	Some field bodies in this specification are defined simply as
416	"unstructured" (which is specified in section 3.2.5 as any printable
417	US-ASCII characters plus white space characters) with no further
418	restrictions. These are referred to as unstructured field bodies.
419	Semantically, unstructured field bodies are simply to be treated as a
420	single line of characters with no further processing (except for
421	"folding" and "unfolding" as described in section 2.2.3).
422
423	2.2.2. Structured Header Field Bodies
424
425	Some field bodies in this specification have a syntax that is more
426	restrictive than the unstructured field bodies described above.
427	These are referred to as "structured" field bodies. Structured field
428	bodies are sequences of specific lexical tokens as described in
429	sections 3 and 4 of this specification. Many of these tokens are
430	allowed (according to their syntax) to be introduced or end with
431	comments (as described in section 3.2.2) as well as the white space
432	characters, and those white space characters are subject to "folding"
433	and "unfolding" as described in section 2.2.3. Semantic analysis of
434	structured field bodies is given along with their syntax.
435
436	2.2.3. Long Header Fields
437
438	Each header field is logically a single line of characters comprising
439	the field name, the colon, and the field body. For convenience
440	however, and to deal with the 998/78 character limitations per line,
441	the field body portion of a header field can be split into a
442	multiple-line representation; this is called "folding". The general
443	rule is that wherever this specification allows for folding white
444	space (not simply WSP characters), a CRLF may be inserted before any
445	WSP.
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454
455	For example, the header field:
456
457	Subject: This is a test
458
459	can be represented as:
460
461	Subject: This
462	is a test
463
464	Note: Though structured field bodies are defined in such a way
465	that folding can take place between many of the lexical tokens
466	(and even within some of the lexical tokens), folding SHOULD be
467	limited to placing the CRLF at higher-level syntactic breaks. For
468	instance, if a field body is defined as comma-separated values, it
469	is recommended that folding occur after the comma separating the
470	structured items in preference to other places where the field
471	could be folded, even if it is allowed elsewhere.
472
473	The process of moving from this folded multiple-line representation
474	of a header field to its single line representation is called
475	"unfolding". Unfolding is accomplished by simply removing any CRLF
476	that is immediately followed by WSP. Each header field should be
477	treated in its unfolded form for further syntactic and semantic
478	evaluation. An unfolded header field has no length restriction and
479	therefore may be indeterminately long.
480
481	2.3. Body
482
483	The body of a message is simply lines of US-ASCII characters. The
484	only two limitations on the body are as follows:
485
486	o CR and LF MUST only occur together as CRLF; they MUST NOT appear
487	independently in the body.
488	o Lines of characters in the body MUST be limited to 998 characters,
489	and SHOULD be limited to 78 characters, excluding the CRLF.
490
491	Note: As was stated earlier, there are other documents,
492	specifically the MIME documents ([RFC2045], [RFC2046], [RFC2049],
493	[RFC4288], [RFC4289]), that extend (and limit) this specification
494	to allow for different sorts of message bodies. Again, these
495	mechanisms are beyond the scope of this document.
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510
511	3. Syntax
512
513	3.1. Introduction
514
515	The syntax as given in this section defines the legal syntax of
516	Internet messages. Messages that are conformant to this
517	specification MUST conform to the syntax in this section. If there
518	are options in this section where one option SHOULD be generated,
519	that is indicated either in the prose or in a comment next to the
520	syntax.
521
522	For the defined expressions, a short description of the syntax and
523	use is given, followed by the syntax in ABNF, followed by a semantic
524	analysis. The following primitive tokens that are used but otherwise
525	unspecified are taken from the "Core Rules" of [RFC5234], Appendix
526	B.1: CR, LF, CRLF, HTAB, SP, WSP, DQUOTE, DIGIT, ALPHA, and VCHAR.
527
528	In some of the definitions, there will be non-terminals whose names
529	start with "obs-". These "obs-" elements refer to tokens defined in
530	the obsolete syntax in section 4. In all cases, these productions
531	are to be ignored for the purposes of generating legal Internet
532	messages and MUST NOT be used as part of such a message. However,
533	when interpreting messages, these tokens MUST be honored as part of
534	the legal syntax. In this sense, section 3 defines a grammar for the
535	generation of messages, with "obs-" elements that are to be ignored,
536	while section 4 adds grammar for the interpretation of messages.
537
538	3.2. Lexical Tokens
539
540	The following rules are used to define an underlying lexical
541	analyzer, which feeds tokens to the higher-level parsers. This
542	section defines the tokens used in structured header field bodies.
543
544	Note: Readers of this specification need to pay special attention
545	to how these lexical tokens are used in both the lower-level and
546	higher-level syntax later in the document. Particularly, the
547	white space tokens and the comment tokens defined in section 3.2.2
548	get used in the lower-level tokens defined here, and those lower-
549	level tokens are in turn used as parts of the higher-level tokens
550	defined later. Therefore, white space and comments may be allowed
551	in the higher-level tokens even though they may not explicitly
552	appear in a particular definition.
553
554	3.2.1. Quoted characters
555
556	Some characters are reserved for special interpretation, such as
557	delimiting lexical tokens. To permit use of these characters as
558	uninterpreted data, a quoting mechanism is provided.
559
560
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566
567	quoted-pair = ("\" (VCHAR / WSP)) / obs-qp
568
569	Where any quoted-pair appears, it is to be interpreted as the
570	character alone. That is to say, the "\" character that appears as
571	part of a quoted-pair is semantically "invisible".
572
573	Note: The "\" character may appear in a message where it is not
574	part of a quoted-pair. A "\" character that does not appear in a
575	quoted-pair is not semantically invisible. The only places in
576	this specification where quoted-pair currently appears are
577	ccontent, qcontent, and in obs-dtext in section 4.
578
579	3.2.2. Folding White Space and Comments
580
581	White space characters, including white space used in folding
582	(described in section 2.2.3), may appear between many elements in
583	header field bodies. Also, strings of characters that are treated as
584	comments may be included in structured field bodies as characters
585	enclosed in parentheses. The following defines the folding white
586	space (FWS) and comment constructs.
587
588	Strings of characters enclosed in parentheses are considered comments
589	so long as they do not appear within a "quoted-string", as defined in
590	section 3.2.4. Comments may nest.
591
592	There are several places in this specification where comments and FWS
593	may be freely inserted. To accommodate that syntax, an additional
594	token for "CFWS" is defined for places where comments and/or FWS can
595	occur. However, where CFWS occurs in this specification, it MUST NOT
596	be inserted in such a way that any line of a folded header field is
597	made up entirely of WSP characters and nothing else.
598
599	FWS = ([*WSP CRLF] 1*WSP) / obs-FWS
600	; Folding white space
601
602	ctext = %d33-39 / ; Printable US-ASCII
603	%d42-91 / ; characters not including
604	%d93-126 / ; "(", ")", or "\"
605	obs-ctext
606
607	ccontent = ctext / quoted-pair / comment
608
609	comment = "(" *([FWS] ccontent) [FWS] ")"
610
611	CFWS = (1*([FWS] comment) [FWS]) / FWS
612
613
614
615
616
617
618	Resnick Standards Track [Page 11]
619
620	RFC 5322 Internet Message Format October 2008
621
622
623	Throughout this specification, where FWS (the folding white space
624	token) appears, it indicates a place where folding, as discussed in
625	section 2.2.3, may take place. Wherever folding appears in a message
626	(that is, a header field body containing a CRLF followed by any WSP),
627	unfolding (removal of the CRLF) is performed before any further
628	semantic analysis is performed on that header field according to this
629	specification. That is to say, any CRLF that appears in FWS is
630	semantically "invisible".
631
632	A comment is normally used in a structured field body to provide some
633	human-readable informational text. Since a comment is allowed to
634	contain FWS, folding is permitted within the comment. Also note that
635	since quoted-pair is allowed in a comment, the parentheses and
636	backslash characters may appear in a comment, so long as they appear
637	as a quoted-pair. Semantically, the enclosing parentheses are not
638	part of the comment; the comment is what is contained between the two
639	parentheses. As stated earlier, the "\" in any quoted-pair and the
640	CRLF in any FWS that appears within the comment are semantically
641	"invisible" and therefore not part of the comment either.
642
643	Runs of FWS, comment, or CFWS that occur between lexical tokens in a
644	structured header field are semantically interpreted as a single
645	space character.
646
647	3.2.3. Atom
648
649	Several productions in structured header field bodies are simply
650	strings of certain basic characters. Such productions are called
651	atoms.
652
653	Some of the structured header field bodies also allow the period
654	character (".", ASCII value 46) within runs of atext. An additional
655	"dot-atom" token is defined for those purposes.
656
657	Note: The "specials" token does not appear anywhere else in this
658	specification. It is simply the visible (i.e., non-control, non-
659	white space) characters that do not appear in atext. It is
660	provided only because it is useful for implementers who use tools
661	that lexically analyze messages. Each of the characters in
662	specials can be used to indicate a tokenization point in lexical
663	analysis.
664
665
666
667
668
669
670
671
672
673
674	Resnick Standards Track [Page 12]
675
676	RFC 5322 Internet Message Format October 2008
677
678
679	atext = ALPHA / DIGIT / ; Printable US-ASCII
680	"!" / "#" / ; characters not including
681	"$" / "%" / ; specials. Used for atoms.
682	"&" / "'" /
683	"*" / "+" /
684	"-" / "/" /
685	"=" / "?" /
686	"^" / "_" /
687	"`" / "{" /
688	"|" / "}" /
689	"~"
690
691	atom = [CFWS] 1*atext [CFWS]
692
693	dot-atom-text = 1*atext *("." 1*atext)
694
695	dot-atom = [CFWS] dot-atom-text [CFWS]
696
697	specials = "(" / ")" / ; Special characters that do
698	"<" / ">" / ; not appear in atext
699	"[" / "]" /
700	":" / ";" /
701	"@" / "\" /
702	"," / "." /
703	DQUOTE
704
705	Both atom and dot-atom are interpreted as a single unit, comprising
706	the string of characters that make it up. Semantically, the optional
707	comments and FWS surrounding the rest of the characters are not part
708	of the atom; the atom is only the run of atext characters in an atom,
709	or the atext and "." characters in a dot-atom.
710
711	3.2.4. Quoted Strings
712
713	Strings of characters that include characters other than those
714	allowed in atoms can be represented in a quoted string format, where
715	the characters are surrounded by quote (DQUOTE, ASCII value 34)
716	characters.
717
718
719
720
721
722
723
724
725
726
727
728
729
730	Resnick Standards Track [Page 13]
731
732	RFC 5322 Internet Message Format October 2008
733
734
735	qtext = %d33 / ; Printable US-ASCII
736	%d35-91 / ; characters not including
737	%d93-126 / ; "\" or the quote character
738	obs-qtext
739
740	qcontent = qtext / quoted-pair
741
742	quoted-string = [CFWS]
743	DQUOTE *([FWS] qcontent) [FWS] DQUOTE
744	[CFWS]
745
746	A quoted-string is treated as a unit. That is, quoted-string is
747	identical to atom, semantically. Since a quoted-string is allowed to
748	contain FWS, folding is permitted. Also note that since quoted-pair
749	is allowed in a quoted-string, the quote and backslash characters may
750	appear in a quoted-string so long as they appear as a quoted-pair.
751
752	Semantically, neither the optional CFWS outside of the quote
753	characters nor the quote characters themselves are part of the
754	quoted-string; the quoted-string is what is contained between the two
755	quote characters. As stated earlier, the "\" in any quoted-pair and
756	the CRLF in any FWS/CFWS that appears within the quoted-string are
757	semantically "invisible" and therefore not part of the quoted-string
758	either.
759
760	3.2.5. Miscellaneous Tokens
761
762	Three additional tokens are defined: word and phrase for combinations
763	of atoms and/or quoted-strings, and unstructured for use in
764	unstructured header fields and in some places within structured
765	header fields.
766
767	word = atom / quoted-string
768
769	phrase = 1*word / obs-phrase
770
771	unstructured = (*([FWS] VCHAR) *WSP) / obs-unstruct
772
773	3.3. Date and Time Specification
774
775	Date and time values occur in several header fields. This section
776	specifies the syntax for a full date and time specification. Though
777	folding white space is permitted throughout the date-time
778	specification, it is RECOMMENDED that a single space be used in each
779	place that FWS appears (whether it is required or optional); some
780	older implementations will not interpret longer sequences of folding
781	white space correctly.
782
783
784
785
786	Resnick Standards Track [Page 14]
787
788	RFC 5322 Internet Message Format October 2008
789
790
791	date-time = [ day-of-week "," ] date time [CFWS]
792
793	day-of-week = ([FWS] day-name) / obs-day-of-week
794
795	day-name = "Mon" / "Tue" / "Wed" / "Thu" /
796	"Fri" / "Sat" / "Sun"
797
798	date = day month year
799
800	day = ([FWS] 1*2DIGIT FWS) / obs-day
801
802	month = "Jan" / "Feb" / "Mar" / "Apr" /
803	"May" / "Jun" / "Jul" / "Aug" /
804	"Sep" / "Oct" / "Nov" / "Dec"
805
806	year = (FWS 4*DIGIT FWS) / obs-year
807
808	time = time-of-day zone
809
810	time-of-day = hour ":" minute [ ":" second ]
811
812	hour = 2DIGIT / obs-hour
813
814	minute = 2DIGIT / obs-minute
815
816	second = 2DIGIT / obs-second
817
818	zone = (FWS ( "+" / "-" ) 4DIGIT) / obs-zone
819
820	The day is the numeric day of the month. The year is any numeric
821	year 1900 or later.
822
823	The time-of-day specifies the number of hours, minutes, and
824	optionally seconds since midnight of the date indicated.
825
826	The date and time-of-day SHOULD express local time.
827
828	The zone specifies the offset from Coordinated Universal Time (UTC,
829	formerly referred to as "Greenwich Mean Time") that the date and
830	time-of-day represent. The "+" or "-" indicates whether the time-of-
831	day is ahead of (i.e., east of) or behind (i.e., west of) Universal
832	Time. The first two digits indicate the number of hours difference
833	from Universal Time, and the last two digits indicate the number of
834	additional minutes difference from Universal Time. (Hence, +hhmm
835	means +(hh * 60 + mm) minutes, and -hhmm means -(hh * 60 + mm)
836	minutes). The form "+0000" SHOULD be used to indicate a time zone at
837	Universal Time. Though "-0000" also indicates Universal Time, it is
838
839
840
841
842	Resnick Standards Track [Page 15]
843
844	RFC 5322 Internet Message Format October 2008
845
846
847	used to indicate that the time was generated on a system that may be
848	in a local time zone other than Universal Time and that the date-time
849	contains no information about the local time zone.
850
851	A date-time specification MUST be semantically valid. That is, the
852	day-of-week (if included) MUST be the day implied by the date, the
853	numeric day-of-month MUST be between 1 and the number of days allowed
854	for the specified month (in the specified year), the time-of-day MUST
855	be in the range 00:00:00 through 23:59:60 (the number of seconds
856	allowing for a leap second; see [RFC1305]), and the last two digits
857	of the zone MUST be within the range 00 through 59.
858
859	3.4. Address Specification
860
861	Addresses occur in several message header fields to indicate senders
862	and recipients of messages. An address may either be an individual
863	mailbox, or a group of mailboxes.
864
865	address = mailbox / group
866
867	mailbox = name-addr / addr-spec
868
869	name-addr = [display-name] angle-addr
870
871	angle-addr = [CFWS] "<" addr-spec ">" [CFWS] /
872	obs-angle-addr
873
874	group = display-name ":" [group-list] ";" [CFWS]
875
876	display-name = phrase
877
878	mailbox-list = (mailbox *("," mailbox)) / obs-mbox-list
879
880	address-list = (address *("," address)) / obs-addr-list
881
882	group-list = mailbox-list / CFWS / obs-group-list
883
884	A mailbox receives mail. It is a conceptual entity that does not
885	necessarily pertain to file storage. For example, some sites may
886	choose to print mail on a printer and deliver the output to the
887	addressee's desk.
888
889	Normally, a mailbox is composed of two parts: (1) an optional display
890	name that indicates the name of the recipient (which can be a person
891	or a system) that could be displayed to the user of a mail
892	application, and (2) an addr-spec address enclosed in angle brackets
893
894
895
896
897
898	Resnick Standards Track [Page 16]
899
900	RFC 5322 Internet Message Format October 2008
901
902
903	("<" and ">"). There is an alternate simple form of a mailbox where
904	the addr-spec address appears alone, without the recipient's name or
905	the angle brackets. The Internet addr-spec address is described in
906	section 3.4.1.
907
908	Note: Some legacy implementations used the simple form where the
909	addr-spec appears without the angle brackets, but included the
910	name of the recipient in parentheses as a comment following the
911	addr-spec. Since the meaning of the information in a comment is
912	unspecified, implementations SHOULD use the full name-addr form of
913	the mailbox, instead of the legacy form, to specify the display
914	name associated with a mailbox. Also, because some legacy
915	implementations interpret the comment, comments generally SHOULD
916	NOT be used in address fields to avoid confusing such
917	implementations.
918
919	When it is desirable to treat several mailboxes as a single unit
920	(i.e., in a distribution list), the group construct can be used. The
921	group construct allows the sender to indicate a named group of
922	recipients. This is done by giving a display name for the group,
923	followed by a colon, followed by a comma-separated list of any number
924	of mailboxes (including zero and one), and ending with a semicolon.
925	Because the list of mailboxes can be empty, using the group construct
926	is also a simple way to communicate to recipients that the message
927	was sent to one or more named sets of recipients, without actually
928	providing the individual mailbox address for any of those recipients.
929
930	3.4.1. Addr-Spec Specification
931
932	An addr-spec is a specific Internet identifier that contains a
933	locally interpreted string followed by the at-sign character ("@",
934	ASCII value 64) followed by an Internet domain. The locally
935	interpreted string is either a quoted-string or a dot-atom. If the
936	string can be represented as a dot-atom (that is, it contains no
937	characters other than atext characters or "." surrounded by atext
938	characters), then the dot-atom form SHOULD be used and the quoted-
939	string form SHOULD NOT be used. Comments and folding white space
940	SHOULD NOT be used around the "@" in the addr-spec.
941
942	Note: A liberal syntax for the domain portion of addr-spec is
943	given here. However, the domain portion contains addressing
944	information specified by and used in other protocols (e.g.,
945	[RFC1034], [RFC1035], [RFC1123], [RFC5321]). It is therefore
946	incumbent upon implementations to conform to the syntax of
947	addresses for the context in which they are used.
948
949
950
951
952
953
954	Resnick Standards Track [Page 17]
955
956	RFC 5322 Internet Message Format October 2008
957
958
959	addr-spec = local-part "@" domain
960
961	local-part = dot-atom / quoted-string / obs-local-part
962
963	domain = dot-atom / domain-literal / obs-domain
964
965	domain-literal = [CFWS] "[" *([FWS] dtext) [FWS] "]" [CFWS]
966
967	dtext = %d33-90 / ; Printable US-ASCII
968	%d94-126 / ; characters not including
969	obs-dtext ; "[", "]", or "\"
970
971	The domain portion identifies the point to which the mail is
972	delivered. In the dot-atom form, this is interpreted as an Internet
973	domain name (either a host name or a mail exchanger name) as
974	described in [RFC1034], [RFC1035], and [RFC1123]. In the domain-
975	literal form, the domain is interpreted as the literal Internet
976	address of the particular host. In both cases, how addressing is
977	used and how messages are transported to a particular host is covered
978	in separate documents, such as [RFC5321]. These mechanisms are
979	outside of the scope of this document.
980
981	The local-part portion is a domain-dependent string. In addresses,
982	it is simply interpreted on the particular host as a name of a
983	particular mailbox.
984
985	3.5. Overall Message Syntax
986
987	A message consists of header fields, optionally followed by a message
988	body. Lines in a message MUST be a maximum of 998 characters
989	excluding the CRLF, but it is RECOMMENDED that lines be limited to 78
990	characters excluding the CRLF. (See section 2.1.1 for explanation.)
991	In a message body, though all of the characters listed in the text
992	rule MAY be used, the use of US-ASCII control characters (values 1
993	through 8, 11, 12, and 14 through 31) is discouraged since their
994	interpretation by receivers for display is not guaranteed.
995
996	message = (fields / obs-fields)
997	[CRLF body]
998
999	body = (*(*998text CRLF) *998text) / obs-body
1000
1001	text = %d1-9 / ; Characters excluding CR
1002	%d11 / ; and LF
1003	%d12 /
1004	%d14-127
1005
1006
1007
1008
1009
1010	Resnick Standards Track [Page 18]
1011
1012	RFC 5322 Internet Message Format October 2008
1013
1014
1015	The header fields carry most of the semantic information and are
1016	defined in section 3.6. The body is simply a series of lines of text
1017	that are uninterpreted for the purposes of this specification.
1018
1019	3.6. Field Definitions
1020
1021	The header fields of a message are defined here. All header fields
1022	have the same general syntactic structure: a field name, followed by
1023	a colon, followed by the field body. The specific syntax for each
1024	header field is defined in the subsequent sections.
1025
1026	Note: In the ABNF syntax for each field in subsequent sections,
1027	each field name is followed by the required colon. However, for
1028	brevity, sometimes the colon is not referred to in the textual
1029	description of the syntax. It is, nonetheless, required.
1030
1031	It is important to note that the header fields are not guaranteed to
1032	be in a particular order. They may appear in any order, and they
1033	have been known to be reordered occasionally when transported over
1034	the Internet. However, for the purposes of this specification,
1035	header fields SHOULD NOT be reordered when a message is transported
1036	or transformed. More importantly, the trace header fields and resent
1037	header fields MUST NOT be reordered, and SHOULD be kept in blocks
1038	prepended to the message. See sections 3.6.6 and 3.6.7 for more
1039	information.
1040
1041	The only required header fields are the origination date field and
1042	the originator address field(s). All other header fields are
1043	syntactically optional. More information is contained in the table
1044	following this definition.
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066	Resnick Standards Track [Page 19]
1067
1068	RFC 5322 Internet Message Format October 2008
1069
1070
1071	fields = *(trace
1072	*optional-field /
1073	*(resent-date /
1074	resent-from /
1075	resent-sender /
1076	resent-to /
1077	resent-cc /
1078	resent-bcc /
1079	resent-msg-id))
1080	*(orig-date /
1081	from /
1082	sender /
1083	reply-to /
1084	to /
1085	cc /
1086	bcc /
1087	message-id /
1088	in-reply-to /
1089	references /
1090	subject /
1091	comments /
1092	keywords /
1093	optional-field)
1094
1095	The following table indicates limits on the number of times each
1096	field may occur in the header section of a message as well as any
1097	special limitations on the use of those fields. An asterisk ("*")
1098	next to a value in the minimum or maximum column indicates that a
1099	special restriction appears in the Notes column.
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122	Resnick Standards Track [Page 20]
1123
1124	RFC 5322 Internet Message Format October 2008
1125
1126
1127	+----------------+--------+------------+----------------------------+
1128	| Field | Min | Max number | Notes |
1129	| | number | | |
1130	+----------------+--------+------------+----------------------------+
1131	| trace | 0 | unlimited | Block prepended - see |
1132	| | | | 3.6.7 |
1133	| resent-date | 0* | unlimited* | One per block, required if |
1134	| | | | other resent fields are |
1135	| | | | present - see 3.6.6 |
1136	| resent-from | 0 | unlimited* | One per block - see 3.6.6 |
1137	| resent-sender | 0* | unlimited* | One per block, MUST occur |
1138	| | | | with multi-address |
1139	| | | | resent-from - see 3.6.6 |
1140	| resent-to | 0 | unlimited* | One per block - see 3.6.6 |
1141	| resent-cc | 0 | unlimited* | One per block - see 3.6.6 |
1142	| resent-bcc | 0 | unlimited* | One per block - see 3.6.6 |
1143	| resent-msg-id | 0 | unlimited* | One per block - see 3.6.6 |
1144	| orig-date | 1 | 1 | |
1145	| from | 1 | 1 | See sender and 3.6.2 |
1146	| sender | 0* | 1 | MUST occur with |
1147	| | | | multi-address from - see |
1148	| | | | 3.6.2 |
1149	| reply-to | 0 | 1 | |
1150	| to | 0 | 1 | |
1151	| cc | 0 | 1 | |
1152	| bcc | 0 | 1 | |
1153	| message-id | 0* | 1 | SHOULD be present - see |
1154	| | | | 3.6.4 |
1155	| in-reply-to | 0* | 1 | SHOULD occur in some |
1156	| | | | replies - see 3.6.4 |
1157	| references | 0* | 1 | SHOULD occur in some |
1158	| | | | replies - see 3.6.4 |
1159	| subject | 0 | 1 | |
1160	| comments | 0 | unlimited | |
1161	| keywords | 0 | unlimited | |
1162	| optional-field | 0 | unlimited | |
1163	+----------------+--------+------------+----------------------------+
1164
1165	The exact interpretation of each field is described in subsequent
1166	sections.
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178	Resnick Standards Track [Page 21]
1179
1180	RFC 5322 Internet Message Format October 2008
1181
1182
1183	3.6.1. The Origination Date Field
1184
1185	The origination date field consists of the field name "Date" followed
1186	by a date-time specification.
1187
1188	orig-date = "Date:" date-time CRLF
1189
1190	The origination date specifies the date and time at which the creator
1191	of the message indicated that the message was complete and ready to
1192	enter the mail delivery system. For instance, this might be the time
1193	that a user pushes the "send" or "submit" button in an application
1194	program. In any case, it is specifically not intended to convey the
1195	time that the message is actually transported, but rather the time at
1196	which the human or other creator of the message has put the message
1197	into its final form, ready for transport. (For example, a portable
1198	computer user who is not connected to a network might queue a message
1199	for delivery. The origination date is intended to contain the date
1200	and time that the user queued the message, not the time when the user
1201	connected to the network to send the message.)
1202
1203	3.6.2. Originator Fields
1204
1205	The originator fields of a message consist of the from field, the
1206	sender field (when applicable), and optionally the reply-to field.
1207	The from field consists of the field name "From" and a comma-
1208	separated list of one or more mailbox specifications. If the from
1209	field contains more than one mailbox specification in the mailbox-
1210	list, then the sender field, containing the field name "Sender" and a
1211	single mailbox specification, MUST appear in the message. In either
1212	case, an optional reply-to field MAY also be included, which contains
1213	the field name "Reply-To" and a comma-separated list of one or more
1214	addresses.
1215
1216	from = "From:" mailbox-list CRLF
1217
1218	sender = "Sender:" mailbox CRLF
1219
1220	reply-to = "Reply-To:" address-list CRLF
1221
1222	The originator fields indicate the mailbox(es) of the source of the
1223	message. The "From:" field specifies the author(s) of the message,
1224	that is, the mailbox(es) of the person(s) or system(s) responsible
1225	for the writing of the message. The "Sender:" field specifies the
1226	mailbox of the agent responsible for the actual transmission of the
1227	message. For example, if a secretary were to send a message for
1228	another person, the mailbox of the secretary would appear in the
1229	"Sender:" field and the mailbox of the actual author would appear in
1230	the "From:" field. If the originator of the message can be indicated
1231
1232
1233
1234	Resnick Standards Track [Page 22]
1235
1236	RFC 5322 Internet Message Format October 2008
1237
1238
1239	by a single mailbox and the author and transmitter are identical, the
1240	"Sender:" field SHOULD NOT be used. Otherwise, both fields SHOULD
1241	appear.
1242
1243	Note: The transmitter information is always present. The absence
1244	of the "Sender:" field is sometimes mistakenly taken to mean that
1245	the agent responsible for transmission of the message has not been
1246	specified. This absence merely means that the transmitter is
1247	identical to the author and is therefore not redundantly placed
1248	into the "Sender:" field.
1249
1250	The originator fields also provide the information required when
1251	replying to a message. When the "Reply-To:" field is present, it
1252	indicates the address(es) to which the author of the message suggests
1253	that replies be sent. In the absence of the "Reply-To:" field,
1254	replies SHOULD by default be sent to the mailbox(es) specified in the
1255	"From:" field unless otherwise specified by the person composing the
1256	reply.
1257
1258	In all cases, the "From:" field SHOULD NOT contain any mailbox that
1259	does not belong to the author(s) of the message. See also section
1260	3.6.3 for more information on forming the destination addresses for a
1261	reply.
1262
1263	3.6.3. Destination Address Fields
1264
1265	The destination fields of a message consist of three possible fields,
1266	each of the same form: the field name, which is either "To", "Cc", or
1267	"Bcc", followed by a comma-separated list of one or more addresses
1268	(either mailbox or group syntax).
1269
1270	to = "To:" address-list CRLF
1271
1272	cc = "Cc:" address-list CRLF
1273
1274	bcc = "Bcc:" [address-list / CFWS] CRLF
1275
1276	The destination fields specify the recipients of the message. Each
1277	destination field may have one or more addresses, and the addresses
1278	indicate the intended recipients of the message. The only difference
1279	between the three fields is how each is used.
1280
1281	The "To:" field contains the address(es) of the primary recipient(s)
1282	of the message.
1283
1284
1285
1286
1287
1288
1289
1290	Resnick Standards Track [Page 23]
1291
1292	RFC 5322 Internet Message Format October 2008
1293
1294
1295	The "Cc:" field (where the "Cc" means "Carbon Copy" in the sense of
1296	making a copy on a typewriter using carbon paper) contains the
1297	addresses of others who are to receive the message, though the
1298	content of the message may not be directed at them.
1299
1300	The "Bcc:" field (where the "Bcc" means "Blind Carbon Copy") contains
1301	addresses of recipients of the message whose addresses are not to be
1302	revealed to other recipients of the message. There are three ways in
1303	which the "Bcc:" field is used. In the first case, when a message
1304	containing a "Bcc:" field is prepared to be sent, the "Bcc:" line is
1305	removed even though all of the recipients (including those specified
1306	in the "Bcc:" field) are sent a copy of the message. In the second
1307	case, recipients specified in the "To:" and "Cc:" lines each are sent
1308	a copy of the message with the "Bcc:" line removed as above, but the
1309	recipients on the "Bcc:" line get a separate copy of the message
1310	containing a "Bcc:" line. (When there are multiple recipient
1311	addresses in the "Bcc:" field, some implementations actually send a
1312	separate copy of the message to each recipient with a "Bcc:"
1313	containing only the address of that particular recipient.) Finally,
1314	since a "Bcc:" field may contain no addresses, a "Bcc:" field can be
1315	sent without any addresses indicating to the recipients that blind
1316	copies were sent to someone. Which method to use with "Bcc:" fields
1317	is implementation dependent, but refer to the "Security
1318	Considerations" section of this document for a discussion of each.
1319
1320	When a message is a reply to another message, the mailboxes of the
1321	authors of the original message (the mailboxes in the "From:" field)
1322	or mailboxes specified in the "Reply-To:" field (if it exists) MAY
1323	appear in the "To:" field of the reply since these would normally be
1324	the primary recipients of the reply. If a reply is sent to a message
1325	that has destination fields, it is often desirable to send a copy of
1326	the reply to all of the recipients of the message, in addition to the
1327	author. When such a reply is formed, addresses in the "To:" and
1328	"Cc:" fields of the original message MAY appear in the "Cc:" field of
1329	the reply, since these are normally secondary recipients of the
1330	reply. If a "Bcc:" field is present in the original message,
1331	addresses in that field MAY appear in the "Bcc:" field of the reply,
1332	but they SHOULD NOT appear in the "To:" or "Cc:" fields.
1333
1334	Note: Some mail applications have automatic reply commands that
1335	include the destination addresses of the original message in the
1336	destination addresses of the reply. How those reply commands
1337	behave is implementation dependent and is beyond the scope of this
1338	document. In particular, whether or not to include the original
1339	destination addresses when the original message had a "Reply-To:"
1340	field is not addressed here.
1341
1342
1343
1344
1345
1346	Resnick Standards Track [Page 24]
1347
1348	RFC 5322 Internet Message Format October 2008
1349
1350
1351	3.6.4. Identification Fields
1352
1353	Though listed as optional in the table in section 3.6, every message
1354	SHOULD have a "Message-ID:" field. Furthermore, reply messages
1355	SHOULD have "In-Reply-To:" and "References:" fields as appropriate
1356	and as described below.
1357
1358	The "Message-ID:" field contains a single unique message identifier.
1359	The "References:" and "In-Reply-To:" fields each contain one or more
1360	unique message identifiers, optionally separated by CFWS.
1361
1362	The message identifier (msg-id) syntax is a limited version of the
1363	addr-spec construct enclosed in the angle bracket characters, "<" and
1364	">". Unlike addr-spec, this syntax only permits the dot-atom-text
1365	form on the left-hand side of the "@" and does not have internal CFWS
1366	anywhere in the message identifier.
1367
1368	Note: As with addr-spec, a liberal syntax is given for the right-
1369	hand side of the "@" in a msg-id. However, later in this section,
1370	the use of a domain for the right-hand side of the "@" is
1371	RECOMMENDED. Again, the syntax of domain constructs is specified
1372	by and used in other protocols (e.g., [RFC1034], [RFC1035],
1373	[RFC1123], [RFC5321]). It is therefore incumbent upon
1374	implementations to conform to the syntax of addresses for the
1375	context in which they are used.
1376
1377	message-id = "Message-ID:" msg-id CRLF
1378
1379	in-reply-to = "In-Reply-To:" 1*msg-id CRLF
1380
1381	references = "References:" 1*msg-id CRLF
1382
1383	msg-id = [CFWS] "<" id-left "@" id-right ">" [CFWS]
1384
1385	id-left = dot-atom-text / obs-id-left
1386
1387	id-right = dot-atom-text / no-fold-literal / obs-id-right
1388
1389	no-fold-literal = "[" *dtext "]"
1390
1391	The "Message-ID:" field provides a unique message identifier that
1392	refers to a particular version of a particular message. The
1393	uniqueness of the message identifier is guaranteed by the host that
1394	generates it (see below). This message identifier is intended to be
1395	machine readable and not necessarily meaningful to humans. A message
1396	identifier pertains to exactly one version of a particular message;
1397	subsequent revisions to the message each receive new message
1398	identifiers.
1399
1400
1401
1402	Resnick Standards Track [Page 25]
1403
1404	RFC 5322 Internet Message Format October 2008
1405
1406
1407	Note: There are many instances when messages are "changed", but
1408	those changes do not constitute a new instantiation of that
1409	message, and therefore the message would not get a new message
1410	identifier. For example, when messages are introduced into the
1411	transport system, they are often prepended with additional header
1412	fields such as trace fields (described in section 3.6.7) and
1413	resent fields (described in section 3.6.6). The addition of such
1414	header fields does not change the identity of the message and
1415	therefore the original "Message-ID:" field is retained. In all
1416	cases, it is the meaning that the sender of the message wishes to
1417	convey (i.e., whether this is the same message or a different
1418	message) that determines whether or not the "Message-ID:" field
1419	changes, not any particular syntactic difference that appears (or
1420	does not appear) in the message.
1421
1422	The "In-Reply-To:" and "References:" fields are used when creating a
1423	reply to a message. They hold the message identifier of the original
1424	message and the message identifiers of other messages (for example,
1425	in the case of a reply to a message that was itself a reply). The
1426	"In-Reply-To:" field may be used to identify the message (or
1427	messages) to which the new message is a reply, while the
1428	"References:" field may be used to identify a "thread" of
1429	conversation.
1430
1431	When creating a reply to a message, the "In-Reply-To:" and
1432	"References:" fields of the resultant message are constructed as
1433	follows:
1434
1435	The "In-Reply-To:" field will contain the contents of the
1436	"Message-ID:" field of the message to which this one is a reply (the
1437	"parent message"). If there is more than one parent message, then
1438	the "In-Reply-To:" field will contain the contents of all of the
1439	parents' "Message-ID:" fields. If there is no "Message-ID:" field in
1440	any of the parent messages, then the new message will have no "In-
1441	Reply-To:" field.
1442
1443	The "References:" field will contain the contents of the parent's
1444	"References:" field (if any) followed by the contents of the parent's
1445	"Message-ID:" field (if any). If the parent message does not contain
1446	a "References:" field but does have an "In-Reply-To:" field
1447	containing a single message identifier, then the "References:" field
1448	will contain the contents of the parent's "In-Reply-To:" field
1449	followed by the contents of the parent's "Message-ID:" field (if
1450	any). If the parent has none of the "References:", "In-Reply-To:",
1451	or "Message-ID:" fields, then the new message will have no
1452	"References:" field.
1453
1454
1455
1456
1457
1458	Resnick Standards Track [Page 26]
1459
1460	RFC 5322 Internet Message Format October 2008
1461
1462
1463	Note: Some implementations parse the "References:" field to
1464	display the "thread of the discussion". These implementations
1465	assume that each new message is a reply to a single parent and
1466	hence that they can walk backwards through the "References:" field
1467	to find the parent of each message listed there. Therefore,
1468	trying to form a "References:" field for a reply that has multiple
1469	parents is discouraged; how to do so is not defined in this
1470	document.
1471
1472	The message identifier (msg-id) itself MUST be a globally unique
1473	identifier for a message. The generator of the message identifier
1474	MUST guarantee that the msg-id is unique. There are several
1475	algorithms that can be used to accomplish this. Since the msg-id has
1476	a similar syntax to addr-spec (identical except that quoted strings,
1477	comments, and folding white space are not allowed), a good method is
1478	to put the domain name (or a domain literal IP address) of the host
1479	on which the message identifier was created on the right-hand side of
1480	the "@" (since domain names and IP addresses are normally unique),
1481	and put a combination of the current absolute date and time along
1482	with some other currently unique (perhaps sequential) identifier
1483	available on the system (for example, a process id number) on the
1484	left-hand side. Though other algorithms will work, it is RECOMMENDED
1485	that the right-hand side contain some domain identifier (either of
1486	the host itself or otherwise) such that the generator of the message
1487	identifier can guarantee the uniqueness of the left-hand side within
1488	the scope of that domain.
1489
1490	Semantically, the angle bracket characters are not part of the
1491	msg-id; the msg-id is what is contained between the two angle bracket
1492	characters.
1493
1494	3.6.5. Informational Fields
1495
1496	The informational fields are all optional. The "Subject:" and
1497	"Comments:" fields are unstructured fields as defined in section
1498	2.2.1, and therefore may contain text or folding white space. The
1499	"Keywords:" field contains a comma-separated list of one or more
1500	words or quoted-strings.
1501
1502	subject = "Subject:" unstructured CRLF
1503
1504	comments = "Comments:" unstructured CRLF
1505
1506	keywords = "Keywords:" phrase *("," phrase) CRLF
1507
1508	These three fields are intended to have only human-readable content
1509	with information about the message. The "Subject:" field is the most
1510	common and contains a short string identifying the topic of the
1511
1512
1513
1514	Resnick Standards Track [Page 27]
1515
1516	RFC 5322 Internet Message Format October 2008
1517
1518
1519	message. When used in a reply, the field body MAY start with the
1520	string "Re: " (an abbreviation of the Latin "in re", meaning "in the
1521	matter of") followed by the contents of the "Subject:" field body of
1522	the original message. If this is done, only one instance of the
1523	literal string "Re: " ought to be used since use of other strings or
1524	more than one instance can lead to undesirable consequences. The
1525	"Comments:" field contains any additional comments on the text of the
1526	body of the message. The "Keywords:" field contains a comma-
1527	separated list of important words and phrases that might be useful
1528	for the recipient.
1529
1530	3.6.6. Resent Fields
1531
1532	Resent fields SHOULD be added to any message that is reintroduced by
1533	a user into the transport system. A separate set of resent fields
1534	SHOULD be added each time this is done. All of the resent fields
1535	corresponding to a particular resending of the message SHOULD be
1536	grouped together. Each new set of resent fields is prepended to the
1537	message; that is, the most recent set of resent fields appears
1538	earlier in the message. No other fields in the message are changed
1539	when resent fields are added.
1540
1541	Each of the resent fields corresponds to a particular field elsewhere
1542	in the syntax. For instance, the "Resent-Date:" field corresponds to
1543	the "Date:" field and the "Resent-To:" field corresponds to the "To:"
1544	field. In each case, the syntax for the field body is identical to
1545	the syntax given previously for the corresponding field.
1546
1547	When resent fields are used, the "Resent-From:" and "Resent-Date:"
1548	fields MUST be sent. The "Resent-Message-ID:" field SHOULD be sent.
1549	"Resent-Sender:" SHOULD NOT be used if "Resent-Sender:" would be
1550	identical to "Resent-From:".
1551
1552	resent-date = "Resent-Date:" date-time CRLF
1553
1554	resent-from = "Resent-From:" mailbox-list CRLF
1555
1556	resent-sender = "Resent-Sender:" mailbox CRLF
1557
1558	resent-to = "Resent-To:" address-list CRLF
1559
1560	resent-cc = "Resent-Cc:" address-list CRLF
1561
1562	resent-bcc = "Resent-Bcc:" [address-list / CFWS] CRLF
1563
1564	resent-msg-id = "Resent-Message-ID:" msg-id CRLF
1565
1566
1567
1568
1569
1570	Resnick Standards Track [Page 28]
1571
1572	RFC 5322 Internet Message Format October 2008
1573
1574
1575	Resent fields are used to identify a message as having been
1576	reintroduced into the transport system by a user. The purpose of
1577	using resent fields is to have the message appear to the final
1578	recipient as if it were sent directly by the original sender, with
1579	all of the original fields remaining the same. Each set of resent
1580	fields correspond to a particular resending event. That is, if a
1581	message is resent multiple times, each set of resent fields gives
1582	identifying information for each individual time. Resent fields are
1583	strictly informational. They MUST NOT be used in the normal
1584	processing of replies or other such automatic actions on messages.
1585
1586	Note: Reintroducing a message into the transport system and using
1587	resent fields is a different operation from "forwarding".
1588	"Forwarding" has two meanings: One sense of forwarding is that a
1589	mail reading program can be told by a user to forward a copy of a
1590	message to another person, making the forwarded message the body
1591	of the new message. A forwarded message in this sense does not
1592	appear to have come from the original sender, but is an entirely
1593	new message from the forwarder of the message. Forwarding may
1594	also mean that a mail transport program gets a message and
1595	forwards it on to a different destination for final delivery.
1596	Resent header fields are not intended for use with either type of
1597	forwarding.
1598
1599	The resent originator fields indicate the mailbox of the person(s) or
1600	system(s) that resent the message. As with the regular originator
1601	fields, there are two forms: a simple "Resent-From:" form, which
1602	contains the mailbox of the individual doing the resending, and the
1603	more complex form, when one individual (identified in the "Resent-
1604	Sender:" field) resends a message on behalf of one or more others
1605	(identified in the "Resent-From:" field).
1606
1607	Note: When replying to a resent message, replies behave just as
1608	they would with any other message, using the original "From:",
1609	"Reply-To:", "Message-ID:", and other fields. The resent fields
1610	are only informational and MUST NOT be used in the normal
1611	processing of replies.
1612
1613	The "Resent-Date:" indicates the date and time at which the resent
1614	message is dispatched by the resender of the message. Like the
1615	"Date:" field, it is not the date and time that the message was
1616	actually transported.
1617
1618	The "Resent-To:", "Resent-Cc:", and "Resent-Bcc:" fields function
1619	identically to the "To:", "Cc:", and "Bcc:" fields, respectively,
1620	except that they indicate the recipients of the resent message, not
1621	the recipients of the original message.
1622
1623
1624
1625
1626	Resnick Standards Track [Page 29]
1627
1628	RFC 5322 Internet Message Format October 2008
1629
1630
1631	The "Resent-Message-ID:" field provides a unique identifier for the
1632	resent message.
1633
1634	3.6.7. Trace Fields
1635
1636	The trace fields are a group of header fields consisting of an
1637	optional "Return-Path:" field, and one or more "Received:" fields.
1638	The "Return-Path:" header field contains a pair of angle brackets
1639	that enclose an optional addr-spec. The "Received:" field contains a
1640	(possibly empty) list of tokens followed by a semicolon and a date-
1641	time specification. Each token must be a word, angle-addr, addr-
1642	spec, or a domain. Further restrictions are applied to the syntax of
1643	the trace fields by specifications that provide for their use, such
1644	as [RFC5321].
1645
1646	trace = [return]
1647	1*received
1648
1649	return = "Return-Path:" path CRLF
1650
1651	path = angle-addr / ([CFWS] "<" [CFWS] ">" [CFWS])
1652
1653	received = "Received:" *received-token ";" date-time CRLF
1654
1655	received-token = word / angle-addr / addr-spec / domain
1656
1657	A full discussion of the Internet mail use of trace fields is
1658	contained in [RFC5321]. For the purposes of this specification, the
1659	trace fields are strictly informational, and any formal
1660	interpretation of them is outside of the scope of this document.
1661
1662	3.6.8. Optional Fields
1663
1664	Fields may appear in messages that are otherwise unspecified in this
1665	document. They MUST conform to the syntax of an optional-field.
1666	This is a field name, made up of the printable US-ASCII characters
1667	except SP and colon, followed by a colon, followed by any text that
1668	conforms to the unstructured syntax.
1669
1670	The field names of any optional field MUST NOT be identical to any
1671	field name specified elsewhere in this document.
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682	Resnick Standards Track [Page 30]
1683
1684	RFC 5322 Internet Message Format October 2008
1685
1686
1687	optional-field = field-name ":" unstructured CRLF
1688
1689	field-name = 1*ftext
1690
1691	ftext = %d33-57 / ; Printable US-ASCII
1692	%d59-126 ; characters not including
1693	; ":".
1694
1695	For the purposes of this specification, any optional field is
1696	uninterpreted.
1697
1698	4. Obsolete Syntax
1699
1700	Earlier versions of this specification allowed for different (usually
1701	more liberal) syntax than is allowed in this version. Also, there
1702	have been syntactic elements used in messages on the Internet whose
1703	interpretations have never been documented. Though these syntactic
1704	forms MUST NOT be generated according to the grammar in section 3,
1705	they MUST be accepted and parsed by a conformant receiver. This
1706	section documents many of these syntactic elements. Taking the
1707	grammar in section 3 and adding the definitions presented in this
1708	section will result in the grammar to use for the interpretation of
1709	messages.
1710
1711	Note: This section identifies syntactic forms that any
1712	implementation MUST reasonably interpret. However, there are
1713	certainly Internet messages that do not conform to even the
1714	additional syntax given in this section. The fact that a
1715	particular form does not appear in any section of this document is
1716	not justification for computer programs to crash or for malformed
1717	data to be irretrievably lost by any implementation. It is up to
1718	the implementation to deal with messages robustly.
1719
1720	One important difference between the obsolete (interpreting) and the
1721	current (generating) syntax is that in structured header field bodies
1722	(i.e., between the colon and the CRLF of any structured header
1723	field), white space characters, including folding white space, and
1724	comments could be freely inserted between any syntactic tokens. This
1725	allowed many complex forms that have proven difficult for some
1726	implementations to parse.
1727
1728	Another key difference between the obsolete and the current syntax is
1729	that the rule in section 3.2.2 regarding lines composed entirely of
1730	white space in comments and folding white space does not apply. See
1731	the discussion of folding white space in section 4.2 below.
1732
1733	Finally, certain characters that were formerly allowed in messages
1734	appear in this section. The NUL character (ASCII value 0) was once
1735
1736
1737
1738	Resnick Standards Track [Page 31]
1739
1740	RFC 5322 Internet Message Format October 2008
1741
1742
1743	allowed, but is no longer for compatibility reasons. Similarly, US-
1744	ASCII control characters other than CR, LF, SP, and HTAB (ASCII
1745	values 1 through 8, 11, 12, 14 through 31, and 127) were allowed to
1746	appear in header field bodies. CR and LF were allowed to appear in
1747	messages other than as CRLF; this use is also shown here.
1748
1749	Other differences in syntax and semantics are noted in the following
1750	sections.
1751
1752	4.1. Miscellaneous Obsolete Tokens
1753
1754	These syntactic elements are used elsewhere in the obsolete syntax or
1755	in the main syntax. Bare CR, bare LF, and NUL are added to obs-qp,
1756	obs-body, and obs-unstruct. US-ASCII control characters are added to
1757	obs-qp, obs-unstruct, obs-ctext, and obs-qtext. The period character
1758	is added to obs-phrase. The obs-phrase-list provides for a
1759	(potentially empty) comma-separated list of phrases that may include
1760	"null" elements. That is, there could be two or more commas in such
1761	a list with nothing in between them, or commas at the beginning or
1762	end of the list.
1763
1764	Note: The "period" (or "full stop") character (".") in obs-phrase
1765	is not a form that was allowed in earlier versions of this or any
1766	other specification. Period (nor any other character from
1767	specials) was not allowed in phrase because it introduced a
1768	parsing difficulty distinguishing between phrases and portions of
1769	an addr-spec (see section 4.4). It appears here because the
1770	period character is currently used in many messages in the
1771	display-name portion of addresses, especially for initials in
1772	names, and therefore must be interpreted properly.
1773
1774	obs-NO-WS-CTL = %d1-8 / ; US-ASCII control
1775	%d11 / ; characters that do not
1776	%d12 / ; include the carriage
1777	%d14-31 / ; return, line feed, and
1778	%d127 ; white space characters
1779
1780	obs-ctext = obs-NO-WS-CTL
1781
1782	obs-qtext = obs-NO-WS-CTL
1783
1784	obs-utext = %d0 / obs-NO-WS-CTL / VCHAR
1785
1786	obs-qp = "\" (%d0 / obs-NO-WS-CTL / LF / CR)
1787
1788	obs-body = *((*LF *CR *((%d0 / text) *LF *CR)) / CRLF)
1789
1790	obs-unstruct = *((*LF *CR *(obs-utext *LF *CR)) / FWS)
1791
1792
1793
1794	Resnick Standards Track [Page 32]
1795
1796	RFC 5322 Internet Message Format October 2008
1797
1798
1799	obs-phrase = word *(word / "." / CFWS)
1800
1801	obs-phrase-list = [phrase / CFWS] *("," [phrase / CFWS])
1802
1803	Bare CR and bare LF appear in messages with two different meanings.
1804	In many cases, bare CR or bare LF are used improperly instead of CRLF
1805	to indicate line separators. In other cases, bare CR and bare LF are
1806	used simply as US-ASCII control characters with their traditional
1807	ASCII meanings.
1808
1809	4.2. Obsolete Folding White Space
1810
1811	In the obsolete syntax, any amount of folding white space MAY be
1812	inserted where the obs-FWS rule is allowed. This creates the
1813	possibility of having two consecutive "folds" in a line, and
1814	therefore the possibility that a line which makes up a folded header
1815	field could be composed entirely of white space.
1816
1817	obs-FWS = 1*WSP *(CRLF 1*WSP)
1818
1819	4.3. Obsolete Date and Time
1820
1821	The syntax for the obsolete date format allows a 2 digit year in the
1822	date field and allows for a list of alphabetic time zone specifiers
1823	that were used in earlier versions of this specification. It also
1824	permits comments and folding white space between many of the tokens.
1825
1826	obs-day-of-week = [CFWS] day-name [CFWS]
1827
1828	obs-day = [CFWS] 1*2DIGIT [CFWS]
1829
1830	obs-year = [CFWS] 2*DIGIT [CFWS]
1831
1832	obs-hour = [CFWS] 2DIGIT [CFWS]
1833
1834	obs-minute = [CFWS] 2DIGIT [CFWS]
1835
1836	obs-second = [CFWS] 2DIGIT [CFWS]
1837
1838	obs-zone = "UT" / "GMT" / ; Universal Time
1839	; North American UT
1840	; offsets
1841	"EST" / "EDT" / ; Eastern: - 5/ - 4
1842	"CST" / "CDT" / ; Central: - 6/ - 5
1843	"MST" / "MDT" / ; Mountain: - 7/ - 6
1844	"PST" / "PDT" / ; Pacific: - 8/ - 7
1845	;
1846
1847
1848
1849
1850	Resnick Standards Track [Page 33]
1851
1852	RFC 5322 Internet Message Format October 2008
1853
1854
1855	%d65-73 / ; Military zones - "A"
1856	%d75-90 / ; through "I" and "K"
1857	%d97-105 / ; through "Z", both
1858	%d107-122 ; upper and lower case
1859
1860	Where a two or three digit year occurs in a date, the year is to be
1861	interpreted as follows: If a two digit year is encountered whose
1862	value is between 00 and 49, the year is interpreted by adding 2000,
1863	ending up with a value between 2000 and 2049. If a two digit year is
1864	encountered with a value between 50 and 99, or any three digit year
1865	is encountered, the year is interpreted by adding 1900.
1866
1867	In the obsolete time zone, "UT" and "GMT" are indications of
1868	"Universal Time" and "Greenwich Mean Time", respectively, and are
1869	both semantically identical to "+0000".
1870
1871	The remaining three character zones are the US time zones. The first
1872	letter, "E", "C", "M", or "P" stands for "Eastern", "Central",
1873	"Mountain", and "Pacific". The second letter is either "S" for
1874	"Standard" time, or "D" for "Daylight Savings" (or summer) time.
1875	Their interpretations are as follows:
1876
1877	EDT is semantically equivalent to -0400
1878	EST is semantically equivalent to -0500
1879	CDT is semantically equivalent to -0500
1880	CST is semantically equivalent to -0600
1881	MDT is semantically equivalent to -0600
1882	MST is semantically equivalent to -0700
1883	PDT is semantically equivalent to -0700
1884	PST is semantically equivalent to -0800
1885
1886	The 1 character military time zones were defined in a non-standard
1887	way in [RFC0822] and are therefore unpredictable in their meaning.
1888	The original definitions of the military zones "A" through "I" are
1889	equivalent to "+0100" through "+0900", respectively; "K", "L", and
1890	"M" are equivalent to "+1000", "+1100", and "+1200", respectively;
1891	"N" through "Y" are equivalent to "-0100" through "-1200".
1892	respectively; and "Z" is equivalent to "+0000". However, because of
1893	the error in [RFC0822], they SHOULD all be considered equivalent to
1894	"-0000" unless there is out-of-band information confirming their
1895	meaning.
1896
1897	Other multi-character (usually between 3 and 5) alphabetic time zones
1898	have been used in Internet messages. Any such time zone whose
1899	meaning is not known SHOULD be considered equivalent to "-0000"
1900	unless there is out-of-band information confirming their meaning.
1901
1902
1903
1904
1905
1906	Resnick Standards Track [Page 34]
1907
1908	RFC 5322 Internet Message Format October 2008
1909
1910
1911	4.4. Obsolete Addressing
1912
1913	There are four primary differences in addressing. First, mailbox
1914	addresses were allowed to have a route portion before the addr-spec
1915	when enclosed in "<" and ">". The route is simply a comma-separated
1916	list of domain names, each preceded by "@", and the list terminated
1917	by a colon. Second, CFWS were allowed between the period-separated
1918	elements of local-part and domain (i.e., dot-atom was not used). In
1919	addition, local-part is allowed to contain quoted-string in addition
1920	to just atom. Third, mailbox-list and address-list were allowed to
1921	have "null" members. That is, there could be two or more commas in
1922	such a list with nothing in between them, or commas at the beginning
1923	or end of the list. Finally, US-ASCII control characters and quoted-
1924	pairs were allowed in domain literals and are added here.
1925
1926	obs-angle-addr = [CFWS] "<" obs-route addr-spec ">" [CFWS]
1927
1928	obs-route = obs-domain-list ":"
1929
1930	obs-domain-list = *(CFWS / ",") "@" domain
1931	*("," [CFWS] ["@" domain])
1932
1933	obs-mbox-list = *([CFWS] ",") mailbox *("," [mailbox / CFWS])
1934
1935	obs-addr-list = *([CFWS] ",") address *("," [address / CFWS])
1936
1937	obs-group-list = 1*([CFWS] ",") [CFWS]
1938
1939	obs-local-part = word *("." word)
1940
1941	obs-domain = atom *("." atom)
1942
1943	obs-dtext = obs-NO-WS-CTL / quoted-pair
1944
1945	When interpreting addresses, the route portion SHOULD be ignored.
1946
1947	4.5. Obsolete Header Fields
1948
1949	Syntactically, the primary difference in the obsolete field syntax is
1950	that it allows multiple occurrences of any of the fields and they may
1951	occur in any order. Also, any amount of white space is allowed
1952	before the ":" at the end of the field name.
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962	Resnick Standards Track [Page 35]
1963
1964	RFC 5322 Internet Message Format October 2008
1965
1966
1967	obs-fields = *(obs-return /
1968	obs-received /
1969	obs-orig-date /
1970	obs-from /
1971	obs-sender /
1972	obs-reply-to /
1973	obs-to /
1974	obs-cc /
1975	obs-bcc /
1976	obs-message-id /
1977	obs-in-reply-to /
1978	obs-references /
1979	obs-subject /
1980	obs-comments /
1981	obs-keywords /
1982	obs-resent-date /
1983	obs-resent-from /
1984	obs-resent-send /
1985	obs-resent-rply /
1986	obs-resent-to /
1987	obs-resent-cc /
1988	obs-resent-bcc /
1989	obs-resent-mid /
1990	obs-optional)
1991
1992	Except for destination address fields (described in section 4.5.3),
1993	the interpretation of multiple occurrences of fields is unspecified.
1994	Also, the interpretation of trace fields and resent fields that do
1995	not occur in blocks prepended to the message is unspecified as well.
1996	Unless otherwise noted in the following sections, interpretation of
1997	other fields is identical to the interpretation of their non-obsolete
1998	counterparts in section 3.
1999
2000	4.5.1. Obsolete Origination Date Field
2001
2002	obs-orig-date = "Date" *WSP ":" date-time CRLF
2003
2004	4.5.2. Obsolete Originator Fields
2005
2006	obs-from = "From" *WSP ":" mailbox-list CRLF
2007
2008	obs-sender = "Sender" *WSP ":" mailbox CRLF
2009
2010	obs-reply-to = "Reply-To" *WSP ":" address-list CRLF
2011
2012
2013
2014
2015
2016
2017
2018	Resnick Standards Track [Page 36]
2019
2020	RFC 5322 Internet Message Format October 2008
2021
2022
2023	4.5.3. Obsolete Destination Address Fields
2024
2025	obs-to = "To" *WSP ":" address-list CRLF
2026
2027	obs-cc = "Cc" *WSP ":" address-list CRLF
2028
2029	obs-bcc = "Bcc" *WSP ":"
2030	(address-list / (*([CFWS] ",") [CFWS])) CRLF
2031
2032	When multiple occurrences of destination address fields occur in a
2033	message, they SHOULD be treated as if the address list in the first
2034	occurrence of the field is combined with the address lists of the
2035	subsequent occurrences by adding a comma and concatenating.
2036
2037	4.5.4. Obsolete Identification Fields
2038
2039	The obsolete "In-Reply-To:" and "References:" fields differ from the
2040	current syntax in that they allow phrase (words or quoted strings) to
2041	appear. The obsolete forms of the left and right sides of msg-id
2042	allow interspersed CFWS, making them syntactically identical to
2043	local-part and domain, respectively.
2044
2045	obs-message-id = "Message-ID" *WSP ":" msg-id CRLF
2046
2047	obs-in-reply-to = "In-Reply-To" *WSP ":" *(phrase / msg-id) CRLF
2048
2049	obs-references = "References" *WSP ":" *(phrase / msg-id) CRLF
2050
2051	obs-id-left = local-part
2052
2053	obs-id-right = domain
2054
2055	For purposes of interpretation, the phrases in the "In-Reply-To:" and
2056	"References:" fields are ignored.
2057
2058	Semantically, none of the optional CFWS in the local-part and the
2059	domain is part of the obs-id-left and obs-id-right, respectively.
2060
2061	4.5.5. Obsolete Informational Fields
2062
2063	obs-subject = "Subject" *WSP ":" unstructured CRLF
2064
2065	obs-comments = "Comments" *WSP ":" unstructured CRLF
2066
2067	obs-keywords = "Keywords" *WSP ":" obs-phrase-list CRLF
2068
2069
2070
2071
2072
2073
2074	Resnick Standards Track [Page 37]
2075
2076	RFC 5322 Internet Message Format October 2008
2077
2078
2079	4.5.6. Obsolete Resent Fields
2080
2081	The obsolete syntax adds a "Resent-Reply-To:" field, which consists
2082	of the field name, the optional comments and folding white space, the
2083	colon, and a comma separated list of addresses.
2084
2085	obs-resent-from = "Resent-From" *WSP ":" mailbox-list CRLF
2086
2087	obs-resent-send = "Resent-Sender" *WSP ":" mailbox CRLF
2088
2089	obs-resent-date = "Resent-Date" *WSP ":" date-time CRLF
2090
2091	obs-resent-to = "Resent-To" *WSP ":" address-list CRLF
2092
2093	obs-resent-cc = "Resent-Cc" *WSP ":" address-list CRLF
2094
2095	obs-resent-bcc = "Resent-Bcc" *WSP ":"
2096	(address-list / (*([CFWS] ",") [CFWS])) CRLF
2097
2098	obs-resent-mid = "Resent-Message-ID" *WSP ":" msg-id CRLF
2099
2100	obs-resent-rply = "Resent-Reply-To" *WSP ":" address-list CRLF
2101
2102	As with other resent fields, the "Resent-Reply-To:" field is to be
2103	treated as trace information only.
2104
2105	4.5.7. Obsolete Trace Fields
2106
2107	The obs-return and obs-received are again given here as template
2108	definitions, just as return and received are in section 3. Their
2109	full syntax is given in [RFC5321].
2110
2111	obs-return = "Return-Path" *WSP ":" path CRLF
2112
2113	obs-received = "Received" *WSP ":" *received-token CRLF
2114
2115	4.5.8. Obsolete optional fields
2116
2117	obs-optional = field-name *WSP ":" unstructured CRLF
2118
2119	5. Security Considerations
2120
2121	Care needs to be taken when displaying messages on a terminal or
2122	terminal emulator. Powerful terminals may act on escape sequences
2123	and other combinations of US-ASCII control characters with a variety
2124	of consequences. They can remap the keyboard or permit other
2125	modifications to the terminal that could lead to denial of service or
2126	even damaged data. They can trigger (sometimes programmable)
2127
2128
2129
2130	Resnick Standards Track [Page 38]
2131
2132	RFC 5322 Internet Message Format October 2008
2133
2134
2135	answerback messages that can allow a message to cause commands to be
2136	issued on the recipient's behalf. They can also affect the operation
2137	of terminal attached devices such as printers. Message viewers may
2138	wish to strip potentially dangerous terminal escape sequences from
2139	the message prior to display. However, other escape sequences appear
2140	in messages for useful purposes (cf. [ISO.2022.1994], [RFC2045],
2141	[RFC2046], [RFC2047], [RFC2049], [RFC4288], [RFC4289]) and therefore
2142	should not be stripped indiscriminately.
2143
2144	Transmission of non-text objects in messages raises additional
2145	security issues. These issues are discussed in [RFC2045], [RFC2046],
2146	[RFC2047], [RFC2049], [RFC4288], and [RFC4289].
2147
2148	Many implementations use the "Bcc:" (blind carbon copy) field,
2149	described in section 3.6.3, to facilitate sending messages to
2150	recipients without revealing the addresses of one or more of the
2151	addressees to the other recipients. Mishandling this use of "Bcc:"
2152	may disclose confidential information that could eventually lead to
2153	security problems through knowledge of even the existence of a
2154	particular mail address. For example, if using the first method
2155	described in section 3.6.3, where the "Bcc:" line is removed from the
2156	message, blind recipients have no explicit indication that they have
2157	been sent a blind copy, except insofar as their address does not
2158	appear in the header section of a message. Because of this, one of
2159	the blind addressees could potentially send a reply to all of the
2160	shown recipients and accidentally reveal that the message went to the
2161	blind recipient. When the second method from section 3.6.3 is used,
2162	the blind recipient's address appears in the "Bcc:" field of a
2163	separate copy of the message. If the "Bcc:" field sent contains all
2164	of the blind addressees, all of the "Bcc:" recipients will be seen by
2165	each "Bcc:" recipient. Even if a separate message is sent to each
2166	"Bcc:" recipient with only the individual's address, implementations
2167	still need to be careful to process replies to the message as per
2168	section 3.6.3 so as not to accidentally reveal the blind recipient to
2169	other recipients.
2170
2171	6. IANA Considerations
2172
2173	This document updates the registrations that appeared in [RFC4021]
2174	that referred to the definitions in [RFC2822]. IANA has updated the
2175	Permanent Message Header Field Repository with the following header
2176	fields, in accordance with the procedures set out in [RFC3864].
2177
2178	Header field name: Date
2179	Applicable protocol: Mail
2180	Status: standard
2181	Author/Change controller: IETF
2182	Specification document(s): This document (section 3.6.1)
2183
2184
2185
2186	Resnick Standards Track [Page 39]
2187
2188	RFC 5322 Internet Message Format October 2008
2189
2190
2191	Header field name: From
2192	Applicable protocol: Mail
2193	Status: standard
2194	Author/Change controller: IETF
2195	Specification document(s): This document (section 3.6.2)
2196
2197	Header field name: Sender
2198	Applicable protocol: Mail
2199	Status: standard
2200	Author/Change controller: IETF
2201	Specification document(s): This document (section 3.6.2)
2202
2203	Header field name: Reply-To
2204	Applicable protocol: Mail
2205	Status: standard
2206	Author/Change controller: IETF
2207	Specification document(s): This document (section 3.6.2)
2208
2209	Header field name: To
2210	Applicable protocol: Mail
2211	Status: standard
2212	Author/Change controller: IETF
2213	Specification document(s): This document (section 3.6.3)
2214
2215	Header field name: Cc
2216	Applicable protocol: Mail
2217	Status: standard
2218	Author/Change controller: IETF
2219	Specification document(s): This document (section 3.6.3)
2220
2221	Header field name: Bcc
2222	Applicable protocol: Mail
2223	Status: standard
2224	Author/Change controller: IETF
2225	Specification document(s): This document (section 3.6.3)
2226
2227	Header field name: Message-ID
2228	Applicable protocol: Mail
2229	Status: standard
2230	Author/Change controller: IETF
2231	Specification document(s): This document (section 3.6.4)
2232
2233	Header field name: In-Reply-To
2234	Applicable protocol: Mail
2235	Status: standard
2236	Author/Change controller: IETF
2237	Specification document(s): This document (section 3.6.4)
2238
2239
2240
2241
2242	Resnick Standards Track [Page 40]
2243
2244	RFC 5322 Internet Message Format October 2008
2245
2246
2247	Header field name: References
2248	Applicable protocol: Mail
2249	Status: standard
2250	Author/Change controller: IETF
2251	Specification document(s): This document (section 3.6.4)
2252
2253	Header field name: Subject
2254	Applicable protocol: Mail
2255	Status: standard
2256	Author/Change controller: IETF
2257	Specification document(s): This document (section 3.6.5)
2258
2259	Header field name: Comments
2260	Applicable protocol: Mail
2261	Status: standard
2262	Author/Change controller: IETF
2263	Specification document(s): This document (section 3.6.5)
2264
2265	Header field name: Keywords
2266	Applicable protocol: Mail
2267	Status: standard
2268	Author/Change controller: IETF
2269	Specification document(s): This document (section 3.6.5)
2270
2271	Header field name: Resent-Date
2272	Applicable protocol: Mail
2273	Status: standard
2274	Author/Change controller: IETF
2275	Specification document(s): This document (section 3.6.6)
2276
2277	Header field name: Resent-From
2278	Applicable protocol: Mail
2279	Status: standard
2280	Author/Change controller: IETF
2281	Specification document(s): This document (section 3.6.6)
2282
2283	Header field name: Resent-Sender
2284	Applicable protocol: Mail
2285	Status: standard
2286	Author/Change controller: IETF
2287	Specification document(s): This document (section 3.6.6)
2288
2289	Header field name: Resent-To
2290	Applicable protocol: Mail
2291	Status: standard
2292	Author/Change controller: IETF
2293	Specification document(s): This document (section 3.6.6)
2294
2295
2296
2297
2298	Resnick Standards Track [Page 41]
2299
2300	RFC 5322 Internet Message Format October 2008
2301
2302
2303	Header field name: Resent-Cc
2304	Applicable protocol: Mail
2305	Status: standard
2306	Author/Change controller: IETF
2307	Specification document(s): This document (section 3.6.6)
2308
2309	Header field name: Resent-Bcc
2310	Applicable protocol: Mail
2311	Status: standard
2312	Author/Change controller: IETF
2313	Specification document(s): This document (section 3.6.6)
2314
2315	Header field name: Resent-Reply-To
2316	Applicable protocol: Mail
2317	Status: obsolete
2318	Author/Change controller: IETF
2319	Specification document(s): This document (section 4.5.6)
2320
2321	Header field name: Resent-Message-ID
2322	Applicable protocol: Mail
2323	Status: standard
2324	Author/Change controller: IETF
2325	Specification document(s): This document (section 3.6.6)
2326
2327	Header field name: Return-Path
2328	Applicable protocol: Mail
2329	Status: standard
2330	Author/Change controller: IETF
2331	Specification document(s): This document (section 3.6.7)
2332
2333	Header field name: Received
2334	Applicable protocol: Mail
2335	Status: standard
2336	Author/Change controller: IETF
2337	Specification document(s): This document (section 3.6.7)
2338	Related information: [RFC5321]
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354	Resnick Standards Track [Page 42]
2355
2356	RFC 5322 Internet Message Format October 2008
2357
2358
2359	Appendix A. Example Messages
2360
2361	This section presents a selection of messages. These are intended to
2362	assist in the implementation of this specification, but should not be
2363	taken as normative; that is to say, although the examples in this
2364	section were carefully reviewed, if there happens to be a conflict
2365	between these examples and the syntax described in sections 3 and 4
2366	of this document, the syntax in those sections is to be taken as
2367	correct.
2368
2369	In the text version of this document, messages in this section are
2370	delimited between lines of "----". The "----" lines are not part of
2371	the message itself.
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410	Resnick Standards Track [Page 43]
2411
2412	RFC 5322 Internet Message Format October 2008
2413
2414
2415	Appendix A.1. Addressing Examples
2416
2417	The following are examples of messages that might be sent between two
2418	individuals.
2419
2420	Appendix A.1.1. A Message from One Person to Another with Simple
2421	Addressing
2422
2423	This could be called a canonical message. It has a single author,
2424	John Doe, a single recipient, Mary Smith, a subject, the date, a
2425	message identifier, and a textual message in the body.
2426
2427	----
2428	From: John Doe <jdoe@machine.example>
2429	To: Mary Smith <mary@example.net>
2430	Subject: Saying Hello
2431	Date: Fri, 21 Nov 1997 09:55:06 -0600
2432	Message-ID: <1234@local.machine.example>
2433
2434	This is a message just to say hello.
2435	So, "Hello".
2436	----
2437
2438	If John's secretary Michael actually sent the message, even though
2439	John was the author and replies to this message should go back to
2440	him, the sender field would be used:
2441
2442	----
2443	From: John Doe <jdoe@machine.example>
2444	Sender: Michael Jones <mjones@machine.example>
2445	To: Mary Smith <mary@example.net>
2446	Subject: Saying Hello
2447	Date: Fri, 21 Nov 1997 09:55:06 -0600
2448	Message-ID: <1234@local.machine.example>
2449
2450	This is a message just to say hello.
2451	So, "Hello".
2452	----
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466	Resnick Standards Track [Page 44]
2467
2468	RFC 5322 Internet Message Format October 2008
2469
2470
2471	Appendix A.1.2. Different Types of Mailboxes
2472
2473	This message includes multiple addresses in the destination fields
2474	and also uses several different forms of addresses.
2475
2476	----
2477	From: "Joe Q. Public" <john.q.public@example.com>
2478	To: Mary Smith <mary@x.test>, jdoe@example.org, Who? <one@y.test>
2479	Cc: <boss@nil.test>, "Giant; \"Big\" Box" <sysservices@example.net>
2480	Date: Tue, 1 Jul 2003 10:52:37 +0200
2481	Message-ID: <5678.21-Nov-1997@example.com>
2482
2483	Hi everyone.
2484	----
2485
2486	Note that the display names for Joe Q. Public and Giant; "Big" Box
2487	needed to be enclosed in double-quotes because the former contains
2488	the period and the latter contains both semicolon and double-quote
2489	characters (the double-quote characters appearing as quoted-pair
2490	constructs). Conversely, the display name for Who? could appear
2491	without them because the question mark is legal in an atom. Notice
2492	also that jdoe@example.org and boss@nil.test have no display names
2493	associated with them at all, and jdoe@example.org uses the simpler
2494	address form without the angle brackets.
2495
2496	Appendix A.1.3. Group Addresses
2497
2498	----
2499	From: Pete <pete@silly.example>
2500	To: A Group:Ed Jones <c@a.test>,joe@where.test,John <jdoe@one.test>;
2501	Cc: Undisclosed recipients:;
2502	Date: Thu, 13 Feb 1969 23:32:54 -0330
2503	Message-ID: <testabcd.1234@silly.example>
2504
2505	Testing.
2506	----
2507
2508	In this message, the "To:" field has a single group recipient named
2509	"A Group", which contains 3 addresses, and a "Cc:" field with an
2510	empty group recipient named Undisclosed recipients.
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522	Resnick Standards Track [Page 45]
2523
2524	RFC 5322 Internet Message Format October 2008
2525
2526
2527	Appendix A.2. Reply Messages
2528
2529	The following is a series of three messages that make up a
2530	conversation thread between John and Mary. John first sends a
2531	message to Mary, Mary then replies to John's message, and then John
2532	replies to Mary's reply message.
2533
2534	Note especially the "Message-ID:", "References:", and "In-Reply-To:"
2535	fields in each message.
2536
2537	----
2538	From: John Doe <jdoe@machine.example>
2539	To: Mary Smith <mary@example.net>
2540	Subject: Saying Hello
2541	Date: Fri, 21 Nov 1997 09:55:06 -0600
2542	Message-ID: <1234@local.machine.example>
2543
2544	This is a message just to say hello.
2545	So, "Hello".
2546	----
2547
2548	When sending replies, the Subject field is often retained, though
2549	prepended with "Re: " as described in section 3.6.5.
2550
2551	----
2552	From: Mary Smith <mary@example.net>
2553	To: John Doe <jdoe@machine.example>
2554	Reply-To: "Mary Smith: Personal Account" <smith@home.example>
2555	Subject: Re: Saying Hello
2556	Date: Fri, 21 Nov 1997 10:01:10 -0600
2557	Message-ID: <3456@example.net>
2558	In-Reply-To: <1234@local.machine.example>
2559	References: <1234@local.machine.example>
2560
2561	This is a reply to your hello.
2562	----
2563
2564	Note the "Reply-To:" field in the above message. When John replies
2565	to Mary's message above, the reply should go to the address in the
2566	"Reply-To:" field instead of the address in the "From:" field.
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578	Resnick Standards Track [Page 46]
2579
2580	RFC 5322 Internet Message Format October 2008
2581
2582
2583	----
2584	To: "Mary Smith: Personal Account" <smith@home.example>
2585	From: John Doe <jdoe@machine.example>
2586	Subject: Re: Saying Hello
2587	Date: Fri, 21 Nov 1997 11:00:00 -0600
2588	Message-ID: <abcd.1234@local.machine.test>
2589	In-Reply-To: <3456@example.net>
2590	References: <1234@local.machine.example> <3456@example.net>
2591
2592	This is a reply to your reply.
2593	----
2594
2595	Appendix A.3. Resent Messages
2596
2597	Start with the message that has been used as an example several
2598	times:
2599
2600	----
2601	From: John Doe <jdoe@machine.example>
2602	To: Mary Smith <mary@example.net>
2603	Subject: Saying Hello
2604	Date: Fri, 21 Nov 1997 09:55:06 -0600
2605	Message-ID: <1234@local.machine.example>
2606
2607	This is a message just to say hello.
2608	So, "Hello".
2609	----
2610
2611	Say that Mary, upon receiving this message, wishes to send a copy of
2612	the message to Jane such that (a) the message would appear to have
2613	come straight from John; (b) if Jane replies to the message, the
2614	reply should go back to John; and (c) all of the original
2615	information, like the date the message was originally sent to Mary,
2616	the message identifier, and the original addressee, is preserved. In
2617	this case, resent fields are prepended to the message:
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634	Resnick Standards Track [Page 47]
2635
2636	RFC 5322 Internet Message Format October 2008
2637
2638
2639	----
2640	Resent-From: Mary Smith <mary@example.net>
2641	Resent-To: Jane Brown <j-brown@other.example>
2642	Resent-Date: Mon, 24 Nov 1997 14:22:01 -0800
2643	Resent-Message-ID: <78910@example.net>
2644	From: John Doe <jdoe@machine.example>
2645	To: Mary Smith <mary@example.net>
2646	Subject: Saying Hello
2647	Date: Fri, 21 Nov 1997 09:55:06 -0600
2648	Message-ID: <1234@local.machine.example>
2649
2650	This is a message just to say hello.
2651	So, "Hello".
2652	----
2653
2654	If Jane, in turn, wished to resend this message to another person,
2655	she would prepend her own set of resent header fields to the above
2656	and send that. (Note that for brevity, trace fields are not shown.)
2657
2658	Appendix A.4. Messages with Trace Fields
2659
2660	As messages are sent through the transport system as described in
2661	[RFC5321], trace fields are prepended to the message. The following
2662	is an example of what those trace fields might look like. Note that
2663	there is some folding white space in the first one since these lines
2664	can be long.
2665
2666	----
2667	Received: from x.y.test
2668	by example.net
2669	via TCP
2670	with ESMTP
2671	id ABC12345
2672	for <mary@example.net>; 21 Nov 1997 10:05:43 -0600
2673	Received: from node.example by x.y.test; 21 Nov 1997 10:01:22 -0600
2674	From: John Doe <jdoe@node.example>
2675	To: Mary Smith <mary@example.net>
2676	Subject: Saying Hello
2677	Date: Fri, 21 Nov 1997 09:55:06 -0600
2678	Message-ID: <1234@local.node.example>
2679
2680	This is a message just to say hello.
2681	So, "Hello".
2682	----
2683
2684
2685
2686
2687
2688
2689
2690	Resnick Standards Track [Page 48]
2691
2692	RFC 5322 Internet Message Format October 2008
2693
2694
2695	Appendix A.5. White Space, Comments, and Other Oddities
2696
2697	White space, including folding white space, and comments can be
2698	inserted between many of the tokens of fields. Taking the example
2699	from A.1.3, white space and comments can be inserted into all of the
2700	fields.
2701
2702	----
2703	From: Pete(A nice \) chap) <pete(his account)@silly.test(his host)>
2704	To:A Group(Some people)
2705	:Chris Jones <c@(Chris's host.)public.example>,
2706	joe@example.org,
2707	John <jdoe@one.test> (my dear friend); (the end of the group)
2708	Cc:(Empty list)(start)Hidden recipients :(nobody(that I know)) ;
2709	Date: Thu,
2710	13
2711	Feb
2712	1969
2713	23:32
2714	-0330 (Newfoundland Time)
2715	Message-ID: <testabcd.1234@silly.test>
2716
2717	Testing.
2718	----
2719
2720	The above example is aesthetically displeasing, but perfectly legal.
2721	Note particularly (1) the comments in the "From:" field (including
2722	one that has a ")" character appearing as part of a quoted-pair); (2)
2723	the white space absent after the ":" in the "To:" field as well as
2724	the comment and folding white space after the group name, the special
2725	character (".") in the comment in Chris Jones's address, and the
2726	folding white space before and after "joe@example.org,"; (3) the
2727	multiple and nested comments in the "Cc:" field as well as the
2728	comment immediately following the ":" after "Cc"; (4) the folding
2729	white space (but no comments except at the end) and the missing
2730	seconds in the time of the date field; and (5) the white space before
2731	(but not within) the identifier in the "Message-ID:" field.
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746	Resnick Standards Track [Page 49]
2747
2748	RFC 5322 Internet Message Format October 2008
2749
2750
2751	Appendix A.6. Obsoleted Forms
2752
2753	The following are examples of obsolete (that is, the "MUST NOT
2754	generate") syntactic elements described in section 4 of this
2755	document.
2756
2757	Appendix A.6.1. Obsolete Addressing
2758
2759	Note in the example below the lack of quotes around Joe Q. Public,
2760	the route that appears in the address for Mary Smith, the two commas
2761	that appear in the "To:" field, and the spaces that appear around the
2762	"." in the jdoe address.
2763
2764	----
2765	From: Joe Q. Public <john.q.public@example.com>
2766	To: Mary Smith <@node.test:mary@example.net>, , jdoe@test . example
2767	Date: Tue, 1 Jul 2003 10:52:37 +0200
2768	Message-ID: <5678.21-Nov-1997@example.com>
2769
2770	Hi everyone.
2771	----
2772
2773	Appendix A.6.2. Obsolete Dates
2774
2775	The following message uses an obsolete date format, including a non-
2776	numeric time zone and a two digit year. Note that although the day-
2777	of-week is missing, that is not specific to the obsolete syntax; it
2778	is optional in the current syntax as well.
2779
2780	----
2781	From: John Doe <jdoe@machine.example>
2782	To: Mary Smith <mary@example.net>
2783	Subject: Saying Hello
2784	Date: 21 Nov 97 09:55:06 GMT
2785	Message-ID: <1234@local.machine.example>
2786
2787	This is a message just to say hello.
2788	So, "Hello".
2789	----
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802	Resnick Standards Track [Page 50]
2803
2804	RFC 5322 Internet Message Format October 2008
2805
2806
2807	Appendix A.6.3. Obsolete White Space and Comments
2808
2809	White space and comments can appear between many more elements than
2810	in the current syntax. Also, folding lines that are made up entirely
2811	of white space are legal.
2812
2813	----
2814	From : John Doe <jdoe@machine(comment). example>
2815	To : Mary Smith
2816	__
2817	<mary@example.net>
2818	Subject : Saying Hello
2819	Date : Fri, 21 Nov 1997 09(comment): 55 : 06 -0600
2820	Message-ID : <1234 @ local(blah) .machine .example>
2821
2822	This is a message just to say hello.
2823	So, "Hello".
2824	----
2825
2826	Note especially the second line of the "To:" field. It starts with
2827	two space characters. (Note that "__" represent blank spaces.)
2828	Therefore, it is considered part of the folding, as described in
2829	section 4.2. Also, the comments and white space throughout
2830	addresses, dates, and message identifiers are all part of the
2831	obsolete syntax.
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858	Resnick Standards Track [Page 51]
2859
2860	RFC 5322 Internet Message Format October 2008
2861
2862
2863	Appendix B. Differences from Earlier Specifications
2864
2865	This appendix contains a list of changes that have been made in the
2866	Internet Message Format from earlier specifications, specifically
2867	[RFC0822], [RFC1123], and [RFC2822]. Items marked with an asterisk
2868	(*) below are items which appear in section 4 of this document and
2869	therefore can no longer be generated.
2870
2871	The following are the changes made from [RFC0822] and [RFC1123] to
2872	[RFC2822] that remain in this document:
2873
2874	1. Period allowed in obsolete form of phrase.
2875	2. ABNF moved out of document, now in [RFC5234].
2876	3. Four or more digits allowed for year.
2877	4. Header field ordering (and lack thereof) made explicit.
2878	5. Encrypted header field removed.
2879	6. Specifically allow and give meaning to "-0000" time zone.
2880	7. Folding white space is not allowed between every token.
2881	8. Requirement for destinations removed.
2882	9. Forwarding and resending redefined.
2883	10. Extension header fields no longer specifically called out.
2884	11. ASCII 0 (null) removed.*
2885	12. Folding continuation lines cannot contain only white space.*
2886	13. Free insertion of comments not allowed in date.*
2887	14. Non-numeric time zones not allowed.*
2888	15. Two digit years not allowed.*
2889	16. Three digit years interpreted, but not allowed for generation.*
2890	17. Routes in addresses not allowed.*
2891	18. CFWS within local-parts and domains not allowed.*
2892	19. Empty members of address lists not allowed.*
2893	20. Folding white space between field name and colon not allowed.*
2894	21. Comments between field name and colon not allowed.
2895	22. Tightened syntax of in-reply-to and references.*
2896	23. CFWS within msg-id not allowed.*
2897	24. Tightened semantics of resent fields as informational only.
2898	25. Resent-Reply-To not allowed.*
2899	26. No multiple occurrences of fields (except resent and received).*
2900	27. Free CR and LF not allowed.*
2901	28. Line length limits specified.
2902	29. Bcc more clearly specified.
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914	Resnick Standards Track [Page 52]
2915
2916	RFC 5322 Internet Message Format October 2008
2917
2918
2919	The following are changes from [RFC2822].
2920	1. Assorted typographical/grammatical errors fixed and
2921	clarifications made.
2922	2. Changed "standard" to "document" or "specification" throughout.
2923	3. Made distinction between "header field" and "header section".
2924	4. Removed NO-WS-CTL from ctext, qtext, dtext, and unstructured.*
2925	5. Moved discussion of specials to the "Atom" section. Moved text
2926	to "Overall message syntax" section.
2927	6. Simplified CFWS syntax.
2928	7. Fixed unstructured syntax.
2929	8. Changed date and time syntax to deal with white space in
2930	obsolete date syntax.
2931	9. Removed quoted-pair from domain literals and message
2932	identifiers.*
2933	10. Clarified that other specifications limit domain syntax.
2934	11. Simplified "Bcc:" and "Resent-Bcc:" syntax.
2935	12. Allowed optional-field to appear within trace information.
2936	13. Removed no-fold-quote from msg-id. Clarified syntax
2937	limitations.
2938	14. Generalized "Received:" syntax to fix bugs and move definition
2939	out of this document.
2940	15. Simplified obs-qp. Fixed and simplified obs-utext (which now
2941	only appears in the obsolete syntax). Removed obs-text and obs-
2942	char, adding obs-body.
2943	16. Fixed obsolete date syntax to allow for more (or less) comments
2944	and white space.
2945	17. Fixed all obsolete list syntax (obs-domain-list, obs-mbox-list,
2946	obs-addr-list, obs-phrase-list, and the newly added obs-group-
2947	list).
2948	18. Fixed obs-reply-to syntax.
2949	19. Fixed obs-bcc and obs-resent-bcc to allow empty lists.
2950	20. Removed obs-path.
2951
2952	Appendix C. Acknowledgements
2953
2954	Many people contributed to this document. They included folks who
2955	participated in the Detailed Revision and Update of Messaging
2956	Standards (DRUMS) Working Group of the Internet Engineering Task
2957	Force (IETF), the chair of DRUMS, the Area Directors of the IETF, and
2958	people who simply sent their comments in via email. The editor is
2959	deeply indebted to them all and thanks them sincerely. The below
2960	list includes everyone who sent email concerning both this document
2961	and [RFC2822]. Hopefully, everyone who contributed is named here:
2962
2963	+--------------------+----------------------+---------------------+
2964	| Matti Aarnio | Tanaka Akira | Russ Allbery |
2965	| Eric Allman | Harald Alvestrand | Ran Atkinson |
2966	| Jos Backus | Bruce Balden | Dave Barr |
2967
2968
2969
2970	Resnick Standards Track [Page 53]
2971
2972	RFC 5322 Internet Message Format October 2008
2973
2974
2975	| Alan Barrett | John Beck | J Robert von Behren |
2976	| Jos den Bekker | D J Bernstein | James Berriman |
2977	| Oliver Block | Norbert Bollow | Raj Bose |
2978	| Antony Bowesman | Scott Bradner | Randy Bush |
2979	| Tom Byrer | Bruce Campbell | Larry Campbell |
2980	| W J Carpenter | Michael Chapman | Richard Clayton |
2981	| Maurizio Codogno | Jim Conklin | R Kelley Cook |
2982	| Nathan Coulter | Steve Coya | Mark Crispin |
2983	| Dave Crocker | Matt Curtin | Michael D'Errico |
2984	| Cyrus Daboo | Michael D Dean | Jutta Degener |
2985	| Mark Delany | Steve Dorner | Harold A Driscoll |
2986	| Michael Elkins | Frank Ellerman | Robert Elz |
2987	| Johnny Eriksson | Erik E Fair | Roger Fajman |
2988	| Patrik Faltstrom | Claus Andre Faerber | Barry Finkel |
2989	| Erik Forsberg | Chuck Foster | Paul Fox |
2990	| Klaus M Frank | Ned Freed | Jochen Friedrich |
2991	| Randall C Gellens | Sukvinder Singh Gill | Tim Goodwin |
2992	| Philip Guenther | Arnt Gulbrandsen | Eric A Hall |
2993	| Tony Hansen | John Hawkinson | Philip Hazel |
2994	| Kai Henningsen | Robert Herriot | Paul Hethmon |
2995	| Jim Hill | Alfred Hoenes | Paul E Hoffman |
2996	| Steve Hole | Kari Hurtta | Marco S Hyman |
2997	| Ofer Inbar | Olle Jarnefors | Kevin Johnson |
2998	| Sudish Joseph | Maynard Kang | Prabhat Keni |
2999	| John C Klensin | Graham Klyne | Brad Knowles |
3000	| Shuhei Kobayashi | Peter Koch | Dan Kohn |
3001	| Christian Kuhtz | Anand Kumria | Steen Larsen |
3002	| Eliot Lear | Barry Leiba | Jay Levitt |
3003	| Bruce Lilly | Lars-Johan Liman | Charles Lindsey |
3004	| Pete Loshin | Simon Lyall | Bill Manning |
3005	| John Martin | Mark Martinec | Larry Masinter |
3006	| Denis McKeon | William P McQuillan | Alexey Melnikov |
3007	| Perry E Metzger | Steven Miller | S Moonesamy |
3008	| Keith Moore | John Gardiner Myers | Chris Newman |
3009	| John W Noerenberg | Eric Norman | Mike O'Dell |
3010	| Larry Osterman | Paul Overell | Jacob Palme |
3011	| Michael A Patton | Uzi Paz | Michael A Quinlan |
3012	| Robert Rapplean | Eric S Raymond | Sam Roberts |
3013	| Hugh Sasse | Bart Schaefer | Tom Scola |
3014	| Wolfgang Segmuller | Nick Shelness | John Stanley |
3015	| Einar Stefferud | Jeff Stephenson | Bernard Stern |
3016	| Peter Sylvester | Mark Symons | Eric Thomas |
3017	| Lee Thompson | Karel De Vriendt | Matthew Wall |
3018	| Rolf Weber | Brent B Welch | Dan Wing |
3019	| Jack De Winter | Gregory J Woodhouse | Greg A Woods |
3020	| Kazu Yamamoto | Alain Zahm | Jamie Zawinski |
3021	| Timothy S Zurcher | | |
3022	+--------------------+----------------------+---------------------+
3023
3024
3025
3026	Resnick Standards Track [Page 54]
3027
3028	RFC 5322 Internet Message Format October 2008
3029
3030
3031	7. References
3032
3033	7.1. Normative References
3034
3035	[ANSI.X3-4.1986] American National Standards Institute, "Coded
3036	Character Set - 7-bit American Standard Code for
3037	Information Interchange", ANSI X3.4, 1986.
3038
3039	[RFC1034] Mockapetris, P., "Domain names - concepts and
3040	facilities", STD 13, RFC 1034, November 1987.
3041
3042	[RFC1035] Mockapetris, P., "Domain names - implementation and
3043	specification", STD 13, RFC 1035, November 1987.
3044
3045	[RFC1123] Braden, R., "Requirements for Internet Hosts -
3046	Application and Support", STD 3, RFC 1123,
3047	October 1989.
3048
3049	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
3050	Requirement Levels", BCP 14, RFC 2119, March 1997.
3051
3052	[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for
3053	Syntax Specifications: ABNF", STD 68, RFC 5234,
3054	January 2008.
3055
3056	7.2. Informative References
3057
3058	[RFC0822] Crocker, D., "Standard for the format of ARPA
3059	Internet text messages", STD 11, RFC 822,
3060	August 1982.
3061
3062	[RFC1305] Mills, D., "Network Time Protocol (Version 3)
3063	Specification, Implementation", RFC 1305,
3064	March 1992.
3065
3066	[ISO.2022.1994] International Organization for Standardization,
3067	"Information technology - Character code structure
3068	and extension techniques", ISO Standard 2022, 1994.
3069
3070	[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet
3071	Mail Extensions (MIME) Part One: Format of Internet
3072	Message Bodies", RFC 2045, November 1996.
3073
3074	[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet
3075	Mail Extensions (MIME) Part Two: Media Types",
3076	RFC 2046, November 1996.
3077
3078
3079
3080
3081
3082	Resnick Standards Track [Page 55]
3083
3084	RFC 5322 Internet Message Format October 2008
3085
3086
3087	[RFC2047] Moore, K., "MIME (Multipurpose Internet Mail
3088	Extensions) Part Three: Message Header Extensions
3089	for Non-ASCII Text", RFC 2047, November 1996.
3090
3091	[RFC2049] Freed, N. and N. Borenstein, "Multipurpose Internet
3092	Mail Extensions (MIME) Part Five: Conformance
3093	Criteria and Examples", RFC 2049, November 1996.
3094
3095	[RFC2822] Resnick, P., "Internet Message Format", RFC 2822,
3096	April 2001.
3097
3098	[RFC3864] Klyne, G., Nottingham, M., and J. Mogul,
3099	"Registration Procedures for Message Header
3100	Fields", BCP 90, RFC 3864, September 2004.
3101
3102	[RFC4021] Klyne, G. and J. Palme, "Registration of Mail and
3103	MIME Header Fields", RFC 4021, March 2005.
3104
3105	[RFC4288] Freed, N. and J. Klensin, "Media Type
3106	Specifications and Registration Procedures",
3107	BCP 13, RFC 4288, December 2005.
3108
3109	[RFC4289] Freed, N. and J. Klensin, "Multipurpose Internet
3110	Mail Extensions (MIME) Part Four: Registration
3111	Procedures", BCP 13, RFC 4289, December 2005.
3112
3113	[RFC5321] Klensin, J., "Simple Mail Transfer Protocol",
3114	RFC 5321, October 2008.
3115
3116	Author's Address
3117
3118	Peter W. Resnick (editor)
3119	Qualcomm Incorporated
3120	5775 Morehouse Drive
3121	San Diego, CA 92121-1714
3122	US
3123
3124	Phone: +1 858 651 4478
3125	EMail: presnick@qualcomm.com
3126	URI: http://www.qualcomm.com/~presnick/
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138	Resnick Standards Track [Page 56]
3139
3140	RFC 5322 Internet Message Format October 2008
3141
3142
3143	Full Copyright Statement
3144
3145	Copyright (C) The IETF Trust (2008).
3146
3147	This document is subject to the rights, licenses and restrictions
3148	contained in BCP 78, and except as set forth therein, the authors
3149	retain all their rights.
3150
3151	This document and the information contained herein are provided on an
3152	"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
3153	OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
3154	THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
3155	OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
3156	THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
3157	WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
3158
3159	Intellectual Property
3160
3161	The IETF takes no position regarding the validity or scope of any
3162	Intellectual Property Rights or other rights that might be claimed to
3163	pertain to the implementation or use of the technology described in
3164	this document or the extent to which any license under such rights
3165	might or might not be available; nor does it represent that it has
3166	made any independent effort to identify any such rights. Information
3167	on the procedures with respect to rights in RFC documents can be
3168	found in BCP 78 and BCP 79.
3169
3170	Copies of IPR disclosures made to the IETF Secretariat and any
3171	assurances of licenses to be made available, or the result of an
3172	attempt made to obtain a general license or permission for the use of
3173	such proprietary rights by implementers or users of this
3174	specification can be obtained from the IETF on-line IPR repository at
3175	http://www.ietf.org/ipr.
3176
3177	The IETF invites any interested party to bring to its attention any
3178	copyrights, patents or patent applications, or other proprietary
3179	rights that may cover technology that may be required to implement
3180	this standard. Please address the information to the IETF at
3181	ietf-ipr@ietf.org.
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194	Resnick Standards Track [Page 57]
3195