Postfix Configuration with mydomainname.

sir,

In linux server, we using Postfix(MTA) configuration then send mail from the outlook Express.

Everyday our linux server IP address dynamically changed. So daily I update IP address in my postfix configuration in [mynetwork= ]

otherwise mail not sends from client hosts to server. Hence, I want to Postfix Configure with myDomainname.Then only i will never update my postfix configuration.

I want how to configure postfix with mydomainname...

please give some steps to where the changes will happen from myhostname to mydomainname....