New software: LMTP to UUCP gateway

Bastian Blank - Tue 25 December 2012

I use UUCP to get my mails. It works fine but lacks support for modern SMTP features like DSN. While it may be possible to bolt support into the the rmail part, both the sendmail interface used to submit mails and the Postfix pipe daemon used to extract mail are not able to do so. So I started a small project to get around this problem.

This software uses LMTP to retrieve and SMTP to send all mails. LMTP (a SMTP derivative with support for all extensions) is used to inject mail via a small daemon. The mails are transported using a format similar to batched SMTP to the remote system. It is then injected via SMTP to the local MTA.

Sender

LMTP is used to supply mail. As a SMTP derivative, LMTP inherits support for all the available SMTP extensions. The only difference between LMTP and SMTP is the support for one result per recipient after end-of-data. This allow proper handling and mails with multiple recipients without a queue.

Mails are supplied to a special LMTP server. This server may currently run from inetd or in foreground by itself. A real daemon mode is not yet implemented.

Each mail is submitted to the UUCP queue in its own format. We need to store a lot of meta-data along with the real mail. This data is stored in a custom format.

Protocol

All data is transferred using a custom protocol. It is a SMTP derivative, but it is only used in uni-directional communication, so no responses exists. It uses its own Hello command and supports the SMTP commands MAIL, RCPT and DATA.

This format allows exactly one mail in each file. An EOF ends the mail transaction. Also all data must be in dot-escaped form like in SMTP.

Hello (UHLO)

A sender must start the transaction with this command. It specifies the name of the sender and all requested SMTP extensions.

Syntax:

uhlo = "UHLO" SP ( Domain / address-literal ) *( SP ehlo-keyword ) CRLF

The receiver must check if all requested SMTP extensions are available.

Receiver

Each mail is submitted by the UUCP system. It calls the supplied receiver tool called rumtp. This tool reads the protocol stream and submits the mail to a local SMTP server.

There is no error handling right now in this tool. All errors will create a mail to the local UUCP admin by the UUCP system itself.

License and distribution

This package is licensed GPL 3. It is for new distributed via Alioth.