Block exe's but not in zip's

What am I missing.  I would like to block such attachments like .exe .pif
 
.pif    0       PIF files not allowed per Company security policy
.exe    0       EXE files not allowed per Company security policy

However how can I limit this to not include extracted archives?

-- 
  Ryan Pavely
   Director Research And Development
   Net Access Corporation
   http://www.nac.net/ http://www.15minuteservers.com/



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