In the mailman admin screen, there is a page that says 'Privacy Options'.
Within that screen, down near the bottom is a field that says:
"Hold posts with header value....."
In that field, you can put a list of values. Here's what I have:
Content-Type: text\/html Content-Type: .*multipart\/alternative Content-Transfer-Encoding: base64
That will block alot of crap from making it to the mailing list.
Unfortunately, it results in the message being held for moderator approval, and with the volume of mail that comes in, It's hard to keep up with it.
Jim McQuillan
jam Ltsp org