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        RFC 2821

        Title:      Simple Mail Transfer Protocol
        Author(s):  J. Klensin, Editor
        Status:     Standards Track
        Date:       April 2001
        Mailbox:    klensin@research.att.com
        Pages:      79
        Characters: 192504
        Updates:    1123
        Obsoletes:  821, 974

        I-D Tag:    draft-ietf-drums-smtpupd-13.txt

        URL:        ftp://ftp.rfc-editor.org/in-notes/rfc2821.txt

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,

-  domain name system requirements and implications for mail
   transport from RFC 1035 and RFC 974,

-  the clarifications and applicability statements in RFC 1123,

-  material drawn from the SMTP Extension mechanisms.

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.

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

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 and IMAP.

Additional submission issues are discussed in RFC 2476.

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 discusses message headers, message bodies
and formats and structures for them, and their relationship.

This document is a product of the Detailed Revision/Update of Message
Standards Working Group of the IETF.

This is now a Proposed Standard Protocol.

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.

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