I am using an exchange server 2003 built in sbs2003. Since a while i'm getting security warning when user try's to open attachement directly in outlook. First, i did add the reg key RemoveLevel1 (.tif, .pdf).
Then i went into to HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesMSExchangeWebOWA to verify that no entry was there for PDF and TIF file type, there was none.
I'm a bit in the dark with that one.