I tried this same sort of thing about a year and a half ago and ran into
mail delivery problems as a result. I had (an older version relative to
today) McAfee NetShield (or something like that) that ran in the background
and scanned everything, including email messages (Post.Office--whatever
version came before 3.0) and messages were constantly getting stuck in the
system. Eventually, I found out that it was the NetShield that was causing
it and disabled it (later uninstalled it completely) and everything was
fine afterward. I don't recall how much of a performance hit there was
because of all of the constant scanning, but the end result was that we
were better off leaving the virus scanning up to the customer. Oh, the OS
was/is NT4 Server with whatever servicepack/hotfixes were available at that
time.
Just my 2 cents worth...
Josh Hillman
hillman@talstar.com