newbie: how is email server in a simple network configured?

[picard]

Assume a small company has an email server with the name
mail.companyname.com.

The company also has a single simple router that assigns all computers
on the network an IP address using DHCP. The company does not have a
domain server or wins server.

Can the router be set up to route all traffic for mail.companyname.com
to the email server or must the server be located outside of the
router?

thanks!