Crossplatform virus scanner for Exchange

Does anyone know of a virus scanner or set of virus scanners that will work in a multiplatform environment where both PCs and Mac use Exchange 2000 as the common mail host for internal e-mail and Internet mail. The scanner(s) need to be able to scanand quarantine e-mail to and from clients on both OS and ideally keep themselves up to date with virus signatures automatically.

The Exchange 2000 software runs on a Win 2000 advanced server which is hosted on a dedicated machine in the DMZ behind a firewall.