After some discussions with colleagues and the relevant depts. in my office, I have come to the conclusion that for my Postfix server, I must implement a 'before-queue' filtering. The reason is that with an 'after-queue' filtering, the email would be lost, and the sender (in case it's a false positive) will never realize that.
That is unacceptable for my company; if the 'falsely accused' sender gets a notification, we want him/her to try resending the email through other channels. If he/she doesn't get a notification, he/she won't attempt a re-send.
Now, after perusing the various docs on SpamAssassin, I happened upon more than one way to implement SpamAssassin 'before-queue' filtering. E.g.,
- SA + amavisd-new (run as smtpd proxy)
- SA + amavisd-new + amavisd-milter
- SA + MIMEdefang (run as milter)
- SA + spampd (run as smtpd proxy)
- SA + milter-spamd
... and I'm sure you may also find other ways to implement it.
My question is: Which one(s) of the above is (/are) recommended? Do you know of its pros/cons? Or perhaps do you have something better in mind?
Thanks in advance!