MAIL Parameters

Last Updated

2024-04-25

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Registries included below

• SMTP Service Extensions
  • SMTP Service Extension Parameters
• Mail Transmission Types
  • VIA link types
  • WITH protocol types
  • Additional-registered-clauses
• SMTP PRIORITY extension Priority Assignment Policy
• Registered-states
• Multicast Email SMTP Extensions
• SMTP Server Limits

SMTP Service Extensions

Registration Procedure(s)

Standards Action or IESG-Approved Experimental RFC

Reference

[RFC5321, Section 2.2]

Note

The Simple Mail Transfer Protocol [RFC5321] specifies a set of commands
or services and a general procedure for extending that set. The table
below lists SMTP service extensions. Both message submission [RFC6409]
and mail transfer [RFC5321] may use these extensions unless otherwise
specified.

As specified in [RFC5321] Section 2.2.2, no entry may be made in this
registry that starts in an "X". Entries may be made only for service
extensions (and associated keywords, parameters, or verbs) that are
defined in Standards-Track or Experimental RFCs specifically approved
by the IESG for this purpose.

The server response to a client EHLO command includes a keyword for
each service extension the server implements.  Some of these keywords
have parameters, which are listed in the "SMTP Service Extension
Parameters" registry.
    

Note

The SMTP Extension names/keywords registered in this section are for 
general use. For those specific to Multicast email, see the registry 
for that protocol below.
      

Available Formats

CSV

Mail Transmission Types

Registration Procedure(s)

Standards Action or IESG-Approved Experimental RFC

Reference

[RFC821][RFC822][RFC5321]

Note

The Simple Mail Transfer Protocol [RFC821][RFC5321] and the Standard for
the Format of ARPA Internet Text Messages [RFC822] specify that a set of
"Received" lines will be prepended to the headers of electronic mail
messages as they are transported through the Internet.
These received line may optionally include either or both a "via" phrase
and/or a "with" phrase.  The legal values for the phrases are listed here.
The via phrase is intended to indicate the link or physical medium over
which the message was transferred.  The with phrase is intended to
indicate the protocol or logical process that was used to transfer the
message.
    

SMTP PRIORITY extension Priority Assignment Policy

Registration Procedure(s)

Specification Required

Expert(s)

Unassigned

Reference

[RFC6710]

Available Formats

CSV

Registered-states

Registration Procedure(s)

First Come First Served

Reference

[RFC6729]

Available Formats

CSV

Multicast Email SMTP Extensions

Registration Procedure(s)

Specification Required

Expert(s)

Alexey Melnikov (primary), RFC Independent Submissions Editor (secondary)

Reference

[RFC8494]

Note

Extension names/keywords and status used with Multicast Email; see 
SMTP Service Extensions above for the list for more general use.

Available Formats

CSV

SMTP Server Limits

Registration Procedure(s)

Specification Required

Expert(s)

John Klensin, Murray Kucherawy (backup)

Reference

[RFC9422]

Available Formats

CSV