That argument seems to be inversed. Unless you have a very small
amount of clients, you are always better off doing it serverside.
or unless you have very good virus signature updating systems or very
good control.
Or do you really chase your Laptop users to upgrade their systems?
The laptops I support run Linux. Not windows so it's not an issue. But
moreover you still haven't solved the virus problem by blocking ONLY at
the mail server. Remember all the ms messenger worm propagation? So it
sounds like you're still chasing down your windows workstations and
laptops...
-sv