Title: Simple Mail Transfer Protocol
Author(s): J. Klensin, Ed..
Status: PROPOSED STANDARD
Date: Apr 2001
Length: 192504
Obsoletes: RFC821, RFC974, RFC1869
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
RFC821 [30],
- domain name system requirements and implications for mail
transport from RFC1035 [22] and RFC974 [27],
- the clarifications and applicability statements in RFC1123 [2],
and
- material drawn from the SMTP Extension mechanisms [19].
It obsoletes RFC821, RFC974, and updates RFC1123 (replaces the mail transport materials of RFC1123). However, RFC821 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 RFC821. It also includes some additional material from RFC1123 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 RFC2476
[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.
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