To configure the DNS name or IP address for your incoming mail server in Postini :
Click the Inbound Servers tab
Click Delivery Mgr
For your convenience you should probably create a name in DNS that will track with the current IP address(es) of your mail server(s). If you change the IP address of your mail server in the future, for example if you change to a different ISP, then Postini will automatically continue to work. If you give Postini the IP address for your mail server then you will need to update your Postini configuration any time the IP address of your mail server changes.