Following up on John Angelmo's post that didn't get any responses... There is a howto at http://advosys.ca/papers/postfix-filtering.html on how to run two instances of Postfix and filter incoming and outgoing mail, although I don't think they are using maildrop (at least on the outgoing side).

I haven't tried this myself, but what I wonder is how Maildrop would behave on the outgoing leg, seeing as it is primarily intended to be invoked on the behalf of the user who is getting mail delivered. To get the benefits of Maildrop filtering for outgoing messages, I presume with a little fussing, Postfix can be told to use Maildrop as the outgoing transport agent, given the sender as the user for which it should be invoked. But are there any easy ways to indicate what filters are incoming, and what ones are outgoing? Is Maildrop smart enough to know what to do with the message after it is done filtering (send it out, don't deliver it locally)?

Does anyone have a solution that doesn't involve Maildrop?

Thanks in advance.....

- Paul