It is possible to create exceptions to bypass IMF in Exchange 2003 SP2. The custom exceptions look for certain word or phrases in the body, subject, or both.
See the following URL for details:
http://www.msexchange.org/tutorials/Intelligent-Message-Filter-version-2-IMF-v2.html
Step 1: register dll: regsvr32 Drive_letter:\Program Files\Exchsrvr\bin\MSCFV2\MSExchange.UceContentFilter.dll
Step 2: create xml file: drive_letter:\Program Files\Exchsrvr\bin\MSCFv2\MSExchange.UceContentFilter.xml
Step 3: Restart SMTP Service