A discussion on the ietf-smtp mailinglist made me think and suggest the
following small addition to your draft
To add to the last paragraph of
3.1. Submission Identification
If an MSA host accepts messages on port 25 then DNS-MX records SHOULD NOT point
to this host.
or more extensivly
If a host accepts messages on port 25 for submission only then DNS-MX
RR-records for this domain MUST NOT point to this host.
This is just a small addition to make (even more) clear that MSA's are not
relay or delivery systems.
Please let me know if you agree or why you disagree with it.