I'm looking into Postfix or qmail, but I've
only just started the
research, so I figured I'd see what others are using or
recommend.
Postfix can do content filtering. You can accomplish quite a lot with
HEADER_CHECKS and BODY_CHECKS, which check the incoming messages for certain
patterns, and REJECT them immediately. You can also use various "blacklists"
to weed out a lot of junk. If that isn't good enough, you can feed messages
to a content filter to further check them. With the current version of
postfix (2.0-19) once you send a message to an external content filter,
you're no longer able to REJECT it, but the next release (2.1) of postfix
will allow this.
As for content filters, I use "amavisd" which is a message "unpacker"
(unpacks attachments from the message) and then sends all the parts to
various checkers, such as SpamAssassin, and a variety of virus checkers (if
you install them).
My setup with postfix, amavisd-new, and spamassassin works great. I run it
under Linux Fedora Core 1. I'm not sure if you can get it to work under
NetBSD or not.
Hope this helps. If you want any specific information, such as config files,
etc. feel free to contact me off-list.
- Bob