On 26 Jun 2016, at 16:44, Chip wrote:
I'm wondering if Postfix can do the following easily.
Nope, not *easily*.
It's a real dog to get this setup in Exim.
Or Sendmail, or probably ANY MTA that isn't tightly integrated to robust local delivery, mailstore, and mail access subsystems OR which has a sophisticated flexible mechanism for arbitrary policy definition and enforcement. So I guess if you wrote cf-ese by hand it might be a cinch in Sendmail... But anyway: this is *out of scope* for a pure MTA.
[details elided]
In other words, a database or text list of emails with corresponding acceptable senders needs to be maintained and referenced for each user, I believe, unless a guru here can tell me how to get the flow properly.
To do this with Postfix, you need some sort of external program. The traditional Postfix mechanism would be a policy daemon. In modern Postfix you could do it in a milter such as MIMEDefang which provides a framework for you to create and enforce any policy that you can express in Perl. (which is easier than cf-ese, really...)
Within Postfix proper, I suppose you could hypothetically do this with restriction classes, but those don't scale well. If you had something checking and tagging messages for SPF & DKIM authentication in Postfix (e.g. any mechanism that hooks to SpamAssassin or specialized tools) you could then do delivery via LMTP to something like Dovecot with its Pigeonhole add-on and have all your per-user rules in Sieve rules.
In short: there are many different ways to skin this cat, but they all include the unpleasantry of skinning a cat. Ick.
