Matt forgot about mimedefang. Which I only hear great things about. Otherwise I would go with the milter.
Technically speaking, mimedefang is a milter. But you are correct.. Mimedefang is a pretty cool tool.
Personally I like MailScanner, but that's just based on my liking of the ability to manage the number of inbound MTAs separately from the number of SA scanning processes. High-rate bursts mostly impact my queue depth, not my memory usage.
All the integration tools have their strengths and weaknesses. Pick the one that does what you need.
(One of MailScanner's weaknesses is lack of ability to do a SMTP layer reject based on SA. Something MimeDefang is capable of.)
