Originating Mail Submission Agent (MSA)
The Mail Submission Agent accepts a message from a User
Agent, adds or modifies whatever headers are appropriate
for the message's traversal through the Internet, and
injects the message into the network via a Message
Transfer Agent. An MSA is used, in lieu of the first MTA
by MUA's that do not create fully-compliant Internet mes-
sages, to submit messages into the SMTP delivery network.
The Mail Submission Agent accepts a message from a User
Agent, adds or modifies it as required for Internet standards
and/or site policy, and injects the message into the network.
The MSA may be the initial MTA or may hand off messages to
an MTA.delegate his or her tracking request to a third party by sending them A