Some (re-) submitting system may want to notify receiving system some
extra
information about precedence / priority of messages.
Examples
* Forwarders may run spam filters and know submitting message is
suspicious
* Postcards/'Send-link-to-friends services may know submitting user is
anonymous or may be forged
* Something else
Extension like
MAIL FROM:<user(_at_)somehost(_dot_)dom>
SUBMITTER:<user(_at_)my_spam_markup_forwarder(_dot_)ru>
EXTRA="junk"
will be (imho) useful in this case
List of available must be reserved (may be JUNK, LIST, SUSPICIOUS,
ANONYMOUS, FIRST-CLASS), usage of extra info may be unspecified, receiving
server can interpret extra info by his own rules and/or reputation
services.
A merger of BATV/SPF to protect the RFC 2821 MAIL FROM will not expose an
additional mailbox address as will SUBMITTER. This is important as
SENDER-ID et al will not reduce the amount of spam. In addition, there
will be no means to accredit abuse with SUBMITTER. Unlike a merger of
BATV and SPF, much less of the mail system is damaged as with SUBMITTER.
In general, SUBMITTER is unfriendly.
-Doug