Simple Mail Transfer Protocol
RFC 2821
Document | Type |
RFC - Proposed Standard
(April 2001; Errata)
Obsoleted by RFC 5321
Updated by RFC 5336
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|
---|---|---|---|
Author | John Klensin | ||
Last updated | 2020-01-21 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized with errata bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 2821 (Proposed Standard) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | (None) | ||
Send notices to | (None) |
Network Working Group J. Klensin, Editor Request for Comments: 2821 AT&T Laboratories Obsoletes: 821, 974, 1869 April 2001 Updates: 1123 Category: Standards Track Simple Mail Transfer Protocol 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 (2001). All Rights Reserved. Abstract This document is a self-contained specification of the basic protocol for the Internet electronic mail transport. It consolidates, updates and clarifies, but doesn't add new or change existing functionality of the following: - the original SMTP (Simple Mail Transfer Protocol) specification of RFC 821 [30], - domain name system requirements and implications for mail transport from RFC 1035 [22] and RFC 974 [27], - the clarifications and applicability statements in RFC 1123 [2], and - material drawn from the SMTP Extension mechanisms [19]. It obsoletes RFC 821, RFC 974, and updates RFC 1123 (replaces the mail transport materials of RFC 1123). However, RFC 821 specifies some features that were not in significant use in the Internet by the mid-1990s and (in appendices) some additional transport models. Those sections are omitted here in the interest of clarity and brevity; readers needing them should refer to RFC 821. Klensin Standards Track [Page 1] RFC 2821 Simple Mail Transfer Protocol April 2001 It also includes some additional material from RFC 1123 that required amplification. This material has been identified in multiple ways, mostly by tracking flaming on various lists and newsgroups and problems of unusual readings or interpretations that have appeared as the SMTP extensions have been deployed. Where this specification moves beyond consolidation and actually differs from earlier documents, it supersedes them technically as well as textually. Although SMTP was designed as a mail transport and delivery protocol, this specification also contains information that is important to its use as a 'mail submission' protocol, as recommended for POP [3, 26] and IMAP [6]. Additional submission issues are discussed in RFC 2476 [15]. Section 2.3 provides definitions of terms specific to this document. Except when the historical terminology is necessary for clarity, this document uses the current 'client' and 'server' terminology to identify the sending and receiving SMTP processes, respectively. A companion document [32] discusses message headers, message bodies and formats and structures for them, and their relationship. Table of Contents 1. Introduction .................................................. 4 2. The SMTP Model ................................................ 5 2.1 Basic Structure .............................................. 5 2.2 The Extension Model .......................................... 7 2.2.1 Background ................................................. 7 2.2.2 Definition and Registration of Extensions .................. 8 2.3 Terminology .................................................. 9 2.3.1 Mail Objects ............................................... 10 2.3.2 Senders and Receivers ...................................... 10 2.3.3 Mail Agents and Message Stores ............................. 10 2.3.4 Host ....................................................... 11 2.3.5 Domain ..................................................... 11 2.3.6 Buffer and State Table ..................................... 11 2.3.7 Lines ...................................................... 12 2.3.8 Originator, Delivery, Relay, and Gateway Systems ........... 12 2.3.9 Message Content and Mail Data .............................. 13 2.3.10 Mailbox and Address ....................................... 13 2.3.11 Reply ..................................................... 13 2.4 General Syntax Principles and Transaction Model .............. 13 3. The SMTP Procedures: An Overview .............................. 15 3.1 Session Initiation ........................................... 15 3.2 Client Initiation ............................................ 16 3.3 Mail Transactions ............................................ 16 3.4 Forwarding for Address Correction or Updating ................ 19 Klensin Standards Track [Page 2] RFC 2821 Simple Mail Transfer Protocol April 2001Show full document text