Kevin Schoon 9 months ago

Network Working Group G. Vaudreuil

Request for Comments: 3463 Lucent Technologies

Obsoletes: 1893 January 2003

Category: Standards Track

Enhanced Mail System Status Codes

Status of this Memo

This document specifies an Internet standards track protocol for the

Internet community, and requests discussion and suggestions for

improvements. Please refer to the current edition of the "Internet

Official Protocol Standards" (STD 1) for the standardization state

and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

This document defines a set of extended status codes for use within

the mail system for delivery status reports, tracking, and improved

diagnostics. In combination with other information provided in the

Delivery Status Notification (DSN) delivery report, these codes

facilitate media and language independent rendering of message

delivery status.

Table of Contents

1. Overview ......................................................2

2. Status Code Structure .........................................3

3. Enumerated Status Codes .......................................5

3.1 Other or Undefined Status ...................................6

3.2 Address Status ..............................................6

3.3 Mailbox Status ..............................................7

3.4 Mail system status ..........................................8

3.5 Network and Routing Status ..................................9

3.6 Mail Delivery Protocol Status ..............................10

3.7 Message Content or Message Media Status ....................11

3.8 Security or Policy Status ..................................12

4. References ...................................................13

5. Security Considerations ......................................13

Appendix A - Collected Status Codes ..........................14

Appendix B - Changes from RFC1893 ............................15

Author's Address .............................................15

Full Copyright Statement .....................................16

Vaudreuil Standards Track [Page 1]

RFC 3463 Enhanced Mail System Status Codes January 2003

1. Overview

There is a need for a standard mechanism for the reporting of mail

system errors richer than the limited set offered by SMTP and the

system specific text descriptions sent in mail messages. There is a

pressing need for a rich machine-readable, human language independent

status code for use in delivery status notifications [DSN]. This

document proposes a new set of status codes for this purpose.

SMTP [SMTP] error codes have historically been used for reporting

mail system errors. Because of limitations in the SMTP code design,

these are not suitable for use in delivery status notifications.

SMTP provides about 12 useful codes for delivery reports. The

majority of the codes are protocol specific response codes such as

the 354 response to the SMTP data command. Each of the 12 useful

codes are overloaded to indicate several error conditions. SMTP

suffers some scars from history, most notably the unfortunate damage

to the reply code extension mechanism by uncontrolled use. This

proposal facilitates future extensibility by requiring the client to

interpret unknown error codes according to the theory of codes while

requiring servers to register new response codes.

The SMTP theory of reply codes are partitioned in the number space in

such a manner that the remaining available codes will not provide the

space needed. The most critical example is the existence of only 5

remaining codes for mail system errors. The mail system

classification includes both host and mailbox error conditions. The

remaining third digit space would be completely consumed as needed to

indicate MIME and media conversion errors and security system errors.

A revision to the SMTP theory of reply codes to better distribute the

error conditions in the number space will necessarily be incompatible

with SMTP. Further, consumption of the remaining reply-code number

space for delivery notification reporting will reduce the available

codes for new ESMTP extensions.

The following status code set is based on the SMTP theory of reply

codes. It adopts the success, permanent error, and transient error

semantics of the first value, with a further description and

classification in the second. This proposal re-distributes the

classifications to better distribute the error conditions, such as

separating mailbox from host errors.

Document Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",

"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this

document are to be interpreted as described in BCP 14 [RFC2119].

Vaudreuil Standards Track [Page 2]

RFC 3463 Enhanced Mail System Status Codes January 2003

2. Status Code Structure

This document defines a new set of status codes to report mail system

conditions. These status codes are used for media and language

independent status reporting. They are not intended for system

specific diagnostics.

The syntax of the new status codes is defined as:

status-code = class "." subject "." detail

class = "2"/"4"/"5"

subject = 1*3digit

detail = 1*3digit

White-space characters and comments are NOT allowed within a status-

code. Each numeric sub-code within the status-code MUST be expressed

without leading zero digits.

Status codes consist of three numerical fields separated by ".". The

first sub-code indicates whether the delivery attempt was successful.

The second sub-code indicates the probable source of any delivery

anomalies, and the third sub-code indicates a precise error

condition.

Example: 2.1.23

The code space defined is intended to be extensible only by standards

track documents. Mail system specific status codes should be mapped

as close as possible to the standard status codes. Servers should

send only defined, registered status codes. System specific errors

and diagnostics should be carried by means other than status codes.

New subject and detail codes will be added over time. Because the

number space is large, it is not intended that published status codes

will ever be redefined or eliminated. Clients should preserve the

extensibility of the code space by reporting the general error

described in the subject sub-code when the specific detail is

unrecognized.

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RFC 3463 Enhanced Mail System Status Codes January 2003

The class sub-code provides a broad classification of the status.

The enumerated values for each class are defined as:

2.XXX.XXX Success

Success specifies that the DSN is reporting a positive delivery

action. Detail sub-codes may provide notification of

transformations required for delivery.

4.XXX.XXX Persistent Transient Failure

A persistent transient failure is one in which the message as

sent is valid, but persistence of some temporary condition has

caused abandonment or delay of attempts to send the message.

If this code accompanies a delivery failure report, sending in

the future may be successful.

5.XXX.XXX Permanent Failure

A permanent failure is one which is not likely to be resolved

by resending the message in the current form. Some change to

the message or the destination must be made for successful

delivery.

A client must recognize and report class sub-code even where

subsequent subject sub-codes are unrecognized.

The subject sub-code classifies the status. This value applies to

each of the three classifications. The subject sub-code, if

recognized, must be reported even if the additional detail provided

by the detail sub-code is not recognized. The enumerated values for

the subject sub-code are:

X.0.XXX Other or Undefined Status

There is no additional subject information available.

X.1.XXX Addressing Status

The address status reports on the originator or destination

address. It may include address syntax or validity. These

errors can generally be corrected by the sender and retried.

X.2.XXX Mailbox Status

Mailbox status indicates that something having to do with the

mailbox has caused this DSN. Mailbox issues are assumed to be

under the general control of the recipient.

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RFC 3463 Enhanced Mail System Status Codes January 2003

X.3.XXX Mail System Status

Mail system status indicates that something having to do with

the destination system has caused this DSN. System issues are

assumed to be under the general control of the destination

system administrator.

X.4.XXX Network and Routing Status

The networking or routing codes report status about the

delivery system itself. These system components include any

necessary infrastructure such as directory and routing

services. Network issues are assumed to be under the control

of the destination or intermediate system administrator.

X.5.XXX Mail Delivery Protocol Status

The mail delivery protocol status codes report failures

involving the message delivery protocol. These failures

include the full range of problems resulting from

implementation errors or an unreliable connection.

X.6.XXX Message Content or Media Status

The message content or media status codes report failures

involving the content of the message. These codes report

failures due to translation, transcoding, or otherwise

unsupported message media. Message content or media issues are

under the control of both the sender and the receiver, both of

which must support a common set of supported content-types.

X.7.XXX Security or Policy Status

The security or policy status codes report failures involving

policies such as per-recipient or per-host filtering and

cryptographic operations. Security and policy status issues

are assumed to be under the control of either or both the

sender and recipient. Both the sender and recipient must

permit the exchange of messages and arrange the exchange of

necessary keys and certificates for cryptographic operations.

3. Enumerated Status Codes

The following section defines and describes the detail sub-code. The

detail value provides more information about the status and is

defined relative to the subject of the status.

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RFC 3463 Enhanced Mail System Status Codes January 2003

3.1 Other or Undefined Status

X.0.0 Other undefined Status

Other undefined status is the only undefined error code. It

should be used for all errors for which only the class of the

error is known.

3.2 Address Status

X.1.0 Other address status

Something about the address specified in the message caused

this DSN.

X.1.1 Bad destination mailbox address

The mailbox specified in the address does not exist. For

Internet mail names, this means the address portion to the left

of the "@" sign is invalid. This code is only useful for

permanent failures.

X.1.2 Bad destination system address

The destination system specified in the address does not exist

or is incapable of accepting mail. For Internet mail names,

this means the address portion to the right of the "@" is

invalid for mail. This code is only useful for permanent

failures.

X.1.3 Bad destination mailbox address syntax

The destination address was syntactically invalid. This can

apply to any field in the address. This code is only useful

for permanent failures.

X.1.4 Destination mailbox address ambiguous

The mailbox address as specified matches one or more recipients

on the destination system. This may result if a heuristic

address mapping algorithm is used to map the specified address

to a local mailbox name.

X.1.5 Destination address valid

This mailbox address as specified was valid. This status code

should be used for positive delivery reports.

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RFC 3463 Enhanced Mail System Status Codes January 2003

X.1.6 Destination mailbox has moved, No forwarding address

The mailbox address provided was at one time valid, but mail is

no longer being accepted for that address. This code is only

useful for permanent failures.

X.1.7 Bad sender's mailbox address syntax

The sender's address was syntactically invalid. This can apply

to any field in the address.

X.1.8 Bad sender's system address

The sender's system specified in the address does not exist or

is incapable of accepting return mail. For domain names, this

means the address portion to the right of the "@" is invalid

for mail.

3.3 Mailbox Status

X.2.0 Other or undefined mailbox status

The mailbox exists, but something about the destination mailbox

has caused the sending of this DSN.

X.2.1 Mailbox disabled, not accepting messages

The mailbox exists, but is not accepting messages. This may be

a permanent error if the mailbox will never be re-enabled or a

transient error if the mailbox is only temporarily disabled.

X.2.2 Mailbox full

The mailbox is full because the user has exceeded a per-mailbox

administrative quota or physical capacity. The general

semantics implies that the recipient can delete messages to

make more space available. This code should be used as a

persistent transient failure.

X.2.3 Message length exceeds administrative limit

A per-mailbox administrative message length limit has been

exceeded. This status code should be used when the per-mailbox

message length limit is less than the general system limit.

This code should be used as a permanent failure.

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RFC 3463 Enhanced Mail System Status Codes January 2003

X.2.4 Mailing list expansion problem

The mailbox is a mailing list address and the mailing list was

unable to be expanded. This code may represent a permanent

failure or a persistent transient failure.

3.4 Mail system status

X.3.0 Other or undefined mail system status

The destination system exists and normally accepts mail, but

something about the system has caused the generation of this

DSN.

X.3.1 Mail system full

Mail system storage has been exceeded. The general semantics

imply that the individual recipient may not be able to delete

material to make room for additional messages. This is useful

only as a persistent transient error.

X.3.2 System not accepting network messages

The host on which the mailbox is resident is not accepting

messages. Examples of such conditions include an immanent

shutdown, excessive load, or system maintenance. This is

useful for both permanent and persistent transient errors.

X.3.3 System not capable of selected features

Selected features specified for the message are not supported

by the destination system. This can occur in gateways when

features from one domain cannot be mapped onto the supported

feature in another.

X.3.4 Message too big for system

The message is larger than per-message size limit. This limit

may either be for physical or administrative reasons. This is

useful only as a permanent error.

X.3.5 System incorrectly configured

The system is not configured in a manner that will permit it to

accept this message.

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RFC 3463 Enhanced Mail System Status Codes January 2003

3.5 Network and Routing Status

X.4.0 Other or undefined network or routing status

Something went wrong with the networking, but it is not clear

what the problem is, or the problem cannot be well expressed

with any of the other provided detail codes.

X.4.1 No answer from host

The outbound connection attempt was not answered, because

either the remote system was busy, or was unable to take a

call. This is useful only as a persistent transient error.

X.4.2 Bad connection

The outbound connection was established, but was unable to

complete the message transaction, either because of time-out,

or inadequate connection quality. This is useful only as a

persistent transient error.

X.4.3 Directory server failure

The network system was unable to forward the message, because a

directory server was unavailable. This is useful only as a

persistent transient error.

The inability to connect to an Internet DNS server is one

example of the directory server failure error.

X.4.4 Unable to route

The mail system was unable to determine the next hop for the

message because the necessary routing information was

unavailable from the directory server. This is useful for both

permanent and persistent transient errors.

A DNS lookup returning only an SOA (Start of Administration)

record for a domain name is one example of the unable to route

error.

X.4.5 Mail system congestion

The mail system was unable to deliver the message because the

mail system was congested. This is useful only as a persistent

transient error.

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RFC 3463 Enhanced Mail System Status Codes January 2003

X.4.6 Routing loop detected

A routing loop caused the message to be forwarded too many

times, either because of incorrect routing tables or a user-

forwarding loop. This is useful only as a persistent transient

error.

X.4.7 Delivery time expired

The message was considered too old by the rejecting system,

either because it remained on that host too long or because the

time-to-live value specified by the sender of the message was

exceeded. If possible, the code for the actual problem found

when delivery was attempted should be returned rather than this

code.

3.6 Mail Delivery Protocol Status

X.5.0 Other or undefined protocol status

Something was wrong with the protocol necessary to deliver the

message to the next hop and the problem cannot be well

expressed with any of the other provided detail codes.

X.5.1 Invalid command

A mail transaction protocol command was issued which was either

out of sequence or unsupported. This is useful only as a

permanent error.

X.5.2 Syntax error

A mail transaction protocol command was issued which could not

be interpreted, either because the syntax was wrong or the

command is unrecognized. This is useful only as a permanent

error.

X.5.3 Too many recipients

More recipients were specified for the message than could have

been delivered by the protocol. This error should normally

result in the segmentation of the message into two, the

remainder of the recipients to be delivered on a subsequent

delivery attempt. It is included in this list in the event

that such segmentation is not possible.

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RFC 3463 Enhanced Mail System Status Codes January 2003

X.5.4 Invalid command arguments

A valid mail transaction protocol command was issued with

invalid arguments, either because the arguments were out of

range or represented unrecognized features. This is useful

only as a permanent error.

X.5.5 Wrong protocol version

A protocol version mis-match existed which could not be

automatically resolved by the communicating parties.

3.7 Message Content or Message Media Status

X.6.0 Other or undefined media error

Something about the content of a message caused it to be

considered undeliverable and the problem cannot be well

expressed with any of the other provided detail codes.

X.6.1 Media not supported

The media of the message is not supported by either the

delivery protocol or the next system in the forwarding path.

This is useful only as a permanent error.

X.6.2 Conversion required and prohibited

The content of the message must be converted before it can be

delivered and such conversion is not permitted. Such

prohibitions may be the expression of the sender in the message

itself or the policy of the sending host.

X.6.3 Conversion required but not supported

The message content must be converted in order to be forwarded

but such conversion is not possible or is not practical by a

host in the forwarding path. This condition may result when an

ESMTP gateway supports 8bit transport but is not able to

downgrade the message to 7 bit as required for the next hop.

X.6.4 Conversion with loss performed

This is a warning sent to the sender when message delivery was

successfully but when the delivery required a conversion in

which some data was lost. This may also be a permanent error

if the sender has indicated that conversion with loss is

prohibited for the message.

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RFC 3463 Enhanced Mail System Status Codes January 2003

X.6.5 Conversion Failed

A conversion was required but was unsuccessful. This may be

useful as a permanent or persistent temporary notification.

3.8 Security or Policy Status

X.7.0 Other or undefined security status

Something related to security caused the message to be

returned, and the problem cannot be well expressed with any of

the other provided detail codes. This status code may also be

used when the condition cannot be further described because of

security policies in force.

X.7.1 Delivery not authorized, message refused

The sender is not authorized to send to the destination. This

can be the result of per-host or per-recipient filtering. This

memo does not discuss the merits of any such filtering, but

provides a mechanism to report such. This is useful only as a

permanent error.

X.7.2 Mailing list expansion prohibited

The sender is not authorized to send a message to the intended

mailing list. This is useful only as a permanent error.

X.7.3 Security conversion required but not possible

A conversion from one secure messaging protocol to another was

required for delivery and such conversion was not possible.

This is useful only as a permanent error.

X.7.4 Security features not supported

A message contained security features such as secure

authentication that could not be supported on the delivery

protocol. This is useful only as a permanent error.

X.7.5 Cryptographic failure

A transport system otherwise authorized to validate or decrypt

a message in transport was unable to do so because necessary

information such as key was not available or such information

was invalid.

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RFC 3463 Enhanced Mail System Status Codes January 2003

X.7.6 Cryptographic algorithm not supported

A transport system otherwise authorized to validate or decrypt

a message was unable to do so because the necessary algorithm

was not supported.

X.7.7 Message integrity failure

A transport system otherwise authorized to validate a message

was unable to do so because the message was corrupted or

altered. This may be useful as a permanent, transient

persistent, or successful delivery code.

4. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate

Requirement Levels", BCP 14, RFC 2119, March 1997.

[SMTP] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC

821, August 1982.

[DSN] Moore, K. and G. Vaudreuil, "An Extensible Message Format

for Delivery Status Notifications", RFC 3464, January 2003.

5. Security Considerations

This document describes a status code system with increased

precision. Use of these status codes may disclose additional

information about how an internal mail system is implemented beyond

that currently available.

Vaudreuil Standards Track [Page 13]

RFC 3463 Enhanced Mail System Status Codes January 2003

Appendix A - Collected Status Codes

X.1.0 Other address status

X.1.1 Bad destination mailbox address

X.1.2 Bad destination system address

X.1.3 Bad destination mailbox address syntax

X.1.4 Destination mailbox address ambiguous

X.1.5 Destination mailbox address valid

X.1.6 Mailbox has moved

X.1.7 Bad sender's mailbox address syntax

X.1.8 Bad sender's system address

X.2.0 Other or undefined mailbox status

X.2.1 Mailbox disabled, not accepting messages

X.2.2 Mailbox full

X.2.3 Message length exceeds administrative limit.

X.2.4 Mailing list expansion problem

X.3.0 Other or undefined mail system status

X.3.1 Mail system full

X.3.2 System not accepting network messages

X.3.3 System not capable of selected features

X.3.4 Message too big for system

X.4.0 Other or undefined network or routing status

X.4.1 No answer from host

X.4.2 Bad connection

X.4.3 Routing server failure

X.4.4 Unable to route

X.4.5 Network congestion

X.4.6 Routing loop detected

X.4.7 Delivery time expired

X.5.0 Other or undefined protocol status

X.5.1 Invalid command

X.5.2 Syntax error

X.5.3 Too many recipients

X.5.4 Invalid command arguments

X.5.5 Wrong protocol version

X.6.0 Other or undefined media error

X.6.1 Media not supported

X.6.2 Conversion required and prohibited

X.6.3 Conversion required but not supported

X.6.4 Conversion with loss performed

X.6.5 Conversion failed

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RFC 3463 Enhanced Mail System Status Codes January 2003

X.7.0 Other or undefined security status

X.7.1 Delivery not authorized, message refused

X.7.2 Mailing list expansion prohibited

X.7.3 Security conversion required but not possible

X.7.4 Security features not supported

X.7.5 Cryptographic failure

X.7.6 Cryptographic algorithm not supported

X.7.7 Message integrity failure

Appendix B - Changes from RFC1893

Changed Authors contact information.

Updated required standards boilerplate.

Edited the text to make it spell-checker and grammar checker

compliant.

Modified the text describing the persistent transient failure to more

closely reflect current practice and understanding.

Eliminated the restriction on the X.4.7 codes limiting them to

persistent transient errors.

Author's Address

Gregory M. Vaudreuil

Lucent Technologies

7291 Williamson Rd

Dallas, Tx. 75214

Phone: +1 214 823 9325

EMail: GregV@ieee.org

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RFC 3463 Enhanced Mail System Status Codes January 2003

Full Copyright Statement

Copyright (C) The Internet Society (2003). All Rights Reserved.

This document and translations of it may be copied and furnished to

others, and derivative works that comment on or otherwise explain it

or assist in its implementation may be prepared, copied, published

and distributed, in whole or in part, without restriction of any

kind, provided that the above copyright notice and this paragraph are

included on all such copies and derivative works. However, this

document itself may not be modified in any way, such as by removing

the copyright notice or references to the Internet Society or other

Internet organizations, except as needed for the purpose of

developing Internet standards in which case the procedures for

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followed, or as required to translate it into languages other than

English.

The limited permissions granted above are perpetual and will not be

revoked by the Internet Society or its successors or assigns.

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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING

BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION

HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF

MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

Funding for the RFC Editor function is currently provided by the

Internet Society.

Vaudreuil Standards Track [Page 16]