Local Mail Transfer Protocol
RFC 2033
Document | Type |
RFC - Informational
(October 1996; No errata)
Was draft-myers-lmtp (individual)
|
|
---|---|---|---|
Author | John Myers | ||
Last updated | 2013-03-02 | ||
Stream | Legacy | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | Legacy state | (None) | |
Consensus Boilerplate | Unknown | ||
RFC Editor Note | (None) | ||
IESG | IESG state | RFC 2033 (Informational) | |
Telechat date | |||
Responsible AD | (None) | ||
Send notices to | (None) |
Network Working Group J. Myers Request for Comments: 2033 Carnegie Mellon Category: Informational October 1996 Local Mail Transfer Protocol Status of this Memo This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. Distribution of this memo is unlimited. 1. Abstract SMTP [SMTP] [HOST-REQ] and its service extensions [ESMTP] provide a mechanism for transferring mail reliably and efficiently. The design of the SMTP protocol effectively requires the server to manage a mail delivery queue. In some limited circumstances, outside the area of mail exchange between independent hosts on public networks, it is desirable to implement a system where a mail receiver does not manage a queue. This document describes the LMTP protocol for transporting mail into such systems. Although LMTP is an alternative protocol to ESMTP, it uses (with a few changes) the syntax and semantics of ESMTP. This design permits LMTP to utilize the extensions defined for ESMTP. LMTP should be used only by specific prior arrangement and configuration, and it MUST NOT be used on TCP port 25. Table of Contents 1. Abstract ................................................ 1 2. Conventions Used in this Document ....................... 2 3. Introduction and Overview ............................... 2 4. The LMTP protocol ....................................... 3 4.1. The LHLO, HELO and EHLO commands ........................ 4 4.2. The DATA command ........................................ 4 4.3. The BDAT command ........................................ 5 5. Implementation requirements ............................. 6 6. Acknowledgments ......................................... 6 7. References .............................................. 7 8. Security Considerations ................................. 7 9. Author's Address ........................................ 7 Myers Informational [Page 1] RFC 2033 LMTP October 1996 2. Conventions Used in this Document In examples, "C:" and "S:" indicate lines sent by the client and server respectively. 3. Introduction and Overview The design of the SMTP protocol effectively requires the server to manage a mail delivery queue. This is because a single mail transaction may specify multiple recipients and the final "." of the DATA command may return only one reply code, to indicate the status of the entire transaction. If, for example, a server is given a transaction for two recipients, delivery to the first succeeds, and delivery to the second encounters a temporary failure condition, there is no mechanism to inform the client of the situation. The server must queue the message and later attempt to deliver it to the second recipient. This queuing requirement is beneficial in the situation for which SMTP was originally designed: store-and-forward relay of mail between networked hosts. In some limited situations, it is desirable to have a server which does not manage a queue, instead relying on the client to perform queue management. As an example, consider a hypothetical host with a mail system designed as follows: TCP port 25 +-----------------+ ---------------------->| | ######### | Queue |<># Mail # TCP port 25 | Manager | # Queue # <----------------------| | ######### +-----------------+ Local * ^ Local * Local IPC * | IPC * IPC * | * * | * * | * V | V Non-SMTP +----------+ +----------+ Protocol | Gateway | | Local | ######### <==============>| Delivery | | Delivery |>># Mail # | Agent | | Agent | # Spool # +----------+ +----------+ ######### The host's mail system has three independent, communicating subsystems. The first is a queue manager, which acts as a Myers Informational [Page 2] RFC 2033 LMTP October 1996 traditional SMTP agent, transferring messages to and from other hosts over TCP and managing a mail queue in persistent storage. The otherShow full document text