Please compare what you have written here with the subject of this thread.
I was pointing out that SIEVE is used and can be successfully used for
MTA control. Even if I didn't specifically say "relay control" it may apply.
Specifying filters that are applicable to more than one user, or applicable
to all users, is one thing. Specifying filters that control MTA behavior,
especially behavior as it pertains to detecting and controlling unauthorized
relay attempts, is quite another.
Filters (SIEVE or not) that control MTA behaviour, including relay control
are applicable for all users. I can specify filters for attachments of a
specific
user, domain or all users, at the MTA level. But I'm being picky...
The conflation of sieve with final delivery offers no real impediment to
performing system level actions.
I think SIEVE or extended SIEVE or a MTA specific filtering language
derived from SIEVE or not would be a good thing. It may be a pipe dream
but I think the potential for reducing MTA complexity is there.
Rgds,
-GSH