[Exim] Bulk Mail

In our future set up, we would like to prevent (if possible) bulk mail or
junk mail from outside
our domain. I know there are batch_max and smtp_accept_max_per_host options
available. However, in our case the staff (about 1000) have their own mail
server and all their incoming and outgoing E-Mails would use the mail hub.
Setting these options
may affect the performance of the staff server.

I would be interested what other places have done (or intend to do) to stop
the
bulk e-mailing.

Many thanks

Sujit Choudhury
University of North London
166-220 Holloway Road
London N7 8DB