Windows worms and mail server config

[Pedro Fernandes Macedo]

After those recent freaking virii around , I'm trying to find a way to 
block them...
What's the best way to do this?
I want to avoid sending unnecessary bounces (specially because I'm the 
postmaster for a domain that has about 1300 users and lots of virii 
bounces dailly , which are almost driving me mad, so I want to avoid 
unnecessary pain to other domain admins) ...
Should I just reject messages containing the damned extensions 
(scr,com,pif,bat) or should I accept them , scan them using some 
antivirus and then drop the bounces of infected messages? The second 
option leaves the risk of someone sending a valid pif or bat file that 
has "format c: /X /Q"  , "deltree c: /y" or something like that , but 
leaves the valid e-mails coming... (even though I believe that normal 
windoze users dont send this kind of attachment)...

Right now my server is a standard redhat 9 at work and a FC1 at home , 
both using sendmail... How can I do this?
(hints for qmail and postfix are welcome also , as we're thinking about 
switching from sendmail to qmail or postfix)

Thanx...

Pedro Macedo