What about SpamAssassin filters, and Sendmail Milters that do filtering?
They are not doing the same job as Sieve.
Folks,
Even if they were, I need to repeat that this diagram and this section of the
document are explicitly constrained to formal standards.
It's not that discussing the broader range of pragmatic and equivalent
mechanisms isn't also valuable. It is that it makes the task too large for
this document.
In fact, I think it opens the door to a book, not an IETF architecture
document...
d/
--
Dave Crocker
Brandenburg InternetWorking
bbiw.net