Simple Mail Transfer Protocol

Document Type Replaced Internet-Draft (individual)
Author John Klensin 
Last updated 2020-07-02
Replaced by draft-ietf-emailcore-rfc5321bis
Stream (None)
Intended RFC status (None)
Expired & archived
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Stream Stream state (No stream defined)
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IESG IESG state Replaced by draft-ietf-emailcore-rfc5321bis
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


This document is a specification of the basic protocol for Internet electronic mail transport. It consolidates, updates, and clarifies several previous documents, making all or parts of most of them obsolete. It covers the SMTP extension mechanisms and best practices for the contemporary Internet, but does not provide details about particular extensions. 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 for "split-UA" (User Agent) mail reading systems and mobile environments. This document replaces the earlier version with the same title in RFC 5321. [[CREF1: Note in Draft: Except for the last sentence, the above is unchanged from 5321 and may need adjusting in the light of RFC 6409 as an Internet Standard.]]


John Klensin (

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)