Thanks for the responses! I printed out bunch of Postfix READMEs to read while waiting for my wife and daughter were shopping, and while reading "Before-Queue" and "After-Queue" content filtering README files I was pretty sure that I'd find in my mailbox recommendations to use the content filters. I'll give the After-Queue Content filter a try; it seems to be the best way to go, perhaps utilizing Bennett Todd's SMTP content filtering framework to make the setup simpler.
Though not exacly simple for a newcomer, I find Postfix/Dovecot setup exciting -- unlike with qmail where I often had no idea why something worked the way it did, with Postfix/Dovecot everything can be understood with relative ease. Ville
