I had a talk with a friend the other day and he told me that he does not run MIMEDefang on his systems. Well I do and since most people run MIMEDefang just to be able to run ClamAV and SpamAssassin from one place, I want to explain why. Because when you have a hammer it is better to have more than two nails.
I like running MIMEDefang because it gives me a Perl interpreter at hand and a set of handy routines to manipulate every message that passes through the mail server (header and body). So for any weird idea that I have and I need a proof of concept, I have a full programming language on my email server waiting to run it. And if I have performance issues, well I can always (re)write it in C.
I really think it pays off to invest sometime to learn how to change stuff in mimedefang-filter(5) and how to write your own versions of the filter_* routines.