As the result of repeated requests to make Postfix routing dependent
on envelope or content properties, Postfix now has several mail
delivery features that are not fully orthogonal.
First there are sender_dependent_xxx_maps where xxx is relayhost,
default_transport, and so on. These are "nice" in the sense that
they don't have an effect on mail that should be delivered locally.
Second there is "FILTER transport:". In practice this feature is
suitable only for transit mail. By design the FILTER command
overrides all routing decisions (that is needed for real content
filters to work). However, when filter "FILTER transport:" specifies
an an SMTP client, mail for local recipients will fail with a "mail
loops back to myself" error. This is not obvious from the
documentation and should be added.
So, this is something to be kept in mind when proposing solutions.
Wietse
