msgtrk-model comments

>  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.

I'd suggest using:

                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.


Minor nit: "them" is used with a singular noun in Section 6:

>  delegate his or her tracking
>  request to a third party by sending them A

I think this should be changed to use "it".