I'm pretty sure there must be an easy way to reject or delete mail based on
the filenames of attachments - anything with .exe, .bat, .scr, .vbs, etc.

I'm running sendmail and I have postfix installed but have only dipped a toe
in the complex configuration docs for postfix so far, haven't actually done
anything.  

Postfix looks like it's orientation is end-user operation, not site-wide, is
this correct?