Virtual domain configuration

We have Redhat 6.2 on which we run DNS and internet mail server services. The server is oriented on the DMZ branch of our firewall. We have realized NAT on the firewall. The server is represented with one legal IP adres toward the outside world. Themail server serves currently to www.company1.com domain, where clients can receive and send with adres “name@company1.com”. Now, can we perform another domain definition on the same machine,such as www.company2.com, where clients get adresses of “name@company2.com”? If yes, What are the steps to configure linux? We are using sendmail 8.9.x and qpopper for POP3.