Firewall rules based on DNS?

Hey guys,

I am not a comms guy but have a reasonable understanding of firewalls etc. Is it possible on Cisco based firewalls, to have a rule based on a DNS name? The situation is that our Exchange smart host is an external cluster dns address with a range of addresses in. The addresses sometimes change and therefore I would like a firewall that says, anything from our exchange server on port 25 to cluster.external.address.com should be allowed? I am being told they can only work with IP addresses by our comms guys.

THanks