[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] 
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[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]