Why don't you take an opensource solution? I use a combination of
Postfix+AMaViSd-new+clamav. This works very fine and is secure enough
to give those, who use Windows as Client, a pleasurable and safe
feeling. I didn't tried out this combination under OpenBSD, but I think
this will also work as fine as on Linux Maschines.
Let's call it an accidental feature.
-- Larry Wall