[1] [CITE@en[RFC 4356 - Mapping Between the Multimedia Messaging Service (MMS) and Internet Mail]] ([TIME[2010-12-08 01:37:39 +09:00]] 版) <http://tools.ietf.org/html/rfc4356#section-1.4>

[2] 
>
[PRE[
   MSA     |Message Submission Agent.  A server that accepts messages
           |from User Agents and processes them, either delivering
           |them locally or relaying to an MTA.  See [Submission].
]PRE]

[3] [CITE@en[RFC 4409: Message Submission for Mail]], [TIME[2023-12-02T08:31:39.000Z]], [TIME[2023-12-02T08:47:34.662Z]] <https://www.rfc-editor.org/rfc/rfc4409.html>

[4] [CITE[RFC Errata Report » RFC Editor]], [TIME[2023-12-02T08:47:55.000Z]] <https://www.rfc-editor.org/errata/rfc4409>