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

[2]

   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].

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

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