# maitred

Lightweight embeddable SMTP [RFC5321](https://www.rfc-editor.org/rfc/rfc5321.html)
server for use in applications that need to receive e-mail.

## Use Case

The original goal of this library is to have a usable SMTP server that can be
embedded in mailing list software, particularly for use in
[Ayllu](https://ayllu-forge.org) and 
[Mailpot](https://git.meli-email.org/meli/mailpot). After considering all of
the existing SMTP servers there was no Rust library that could be easily 
embedded in an application and general purpose SMTP servers like Postfix are
too complex to be reasonably packaged.

## Security 

### Relaying

Due to the common abuse of the SMTP protocol by nefarious internet actors the
default behavior of this package must _never_ allow open relaying without 
explicit and conscious configuration from the user. Additionally the SMTP
server must never expose the e-mail addresses or other user data contained
within.

### TLS

This library does not implement any TLS termination nor does it allow for
STARTTLS upgrades. The recommended production setting is to use an SMTP proxy
server like Nginx to terminate TLS there.

## Alpha Status

NOTE: This library is at best in an "alpha" state currently and should be used
for _absolutely nothing_ that is important.

## Protocol Status

### SMTP Base server and Commands [RFC5321](rfcs/rfc5321.txt)

| Name      | Status | Notes                                                 |
|-----------|--------|-------------------------------------------------------|
|  HELO     | ✅     |                                                       |
|  EHLO     | ✅     |                                                       |
|  MAIL     | ✅     |                                                       |
|  RCPT     | ✅     |                                                       |
|  BDAT     | ✅     |                                                       |
|  DATA     | ✅     |                                                       |
|  AUTH     | ✅     |  SASL PLAIN only                                      |
|  VRFY     | ✅     |                                                       |
|  EXPN     | ✅     |                                                       |
|  STARTTLS | ❌     | For the moment there is no plan to implement STARTTLS |


### ESMTP Extensions

| Name                  | Status   | RFC                           |
|-----------------------|----------|-------------------------------|
| SIZE                  | ✅       | [RFC1870](rfcs/rfc1870.txt)   |
| PIPELINING            | ✅       | [RFC2920](rfcs/rfc2920.txt)   |
| 8BITMIME              | ✅       | [RFC6152](rfcs/rfc6152.txt)   |
| ENHANCED STATUS CODES | ⚠️        | [RFC2920](rfcs/rfc3463.txt)   |
| SMTPUTF8              | TODO     | [RFC6531](rfcs/rfc6531.txt)   |
| CHUNKING              | TODO     | [RFC3030](rfcs/rfc3030.txt)   |
| DSN                   | TODO     | [RFC3461](rfcs/rfc3461.txt)   |
| ETRN                  | ❌       | [RFC1985](rfcs/rfc1985.txt)   |
| ATRN                  | ❌       | RFC2645                       |
| BURL                  | ❌       | RFC4468                       |

### Authentication Extensions

All authentication extensions are implemented with the 
[mail-auth](https://crates.io/crates/mail-auth) package from Stalwart.

|name                       | status |
|---------------------------|--------|
| DKIM Verification         | ✅     |
| ARC Chain Verification    | TODO   |
| SPF Policy Evaluation     | TODO   |
| DMARC Policy Evaluation   | TODO   |



## Attributions

Several of the free software libraries released by 
[stalwart](https://github.com/stalwartlabs/mail-server) are in use here.