I don't understand this at all. To the best of my knowledge, there is
no semantic difference between the SenderID and SPFv1 records. They
both have the same features and use the same algorithm. The only
difference is the syntax. Granted, the syntax difference may (but by
no means must) allow for future differences in semantics, but until
that happens, they are, as Jim Lyon pointed out, isomorphic.
Maybe I'm misunderstanding something. Isn't SPF v1 checking the 2821
MAIL-FROM and SenderID checking the SUBMITTER? For an incredible amount
of mail these are not the same thing; the MAIL-FROM is the bounce and
error handler, and the SUBMITTER is the same as the 2822 from (or the
forwarder or the mail server). The MAIL-FROM and the SUBMITTER will
generally be the same for person to person mail, but are not likely to
be the same for either volume or transactional mailings.
A cruise through the headers in my personal mail inbox regularly shows a
rich variety of domain combinations in the return-path and from fields.
Margaret.