Domains - Click on the appropriate domain Manage DNS MX records
Zone: mail.domain.com where mail is the sub domain that is handling your mail.
Value: the first box is for a subdomain of yours that is forwarding your mail to another ip. We recommend using the ipaddress for the new mail server by selecting the second text field and entering the information here.
Mx Priority: this is used for multiple mx records. You can choose which one will handle mail and if it is not available it will go to the next lowest priority mail server designated by another mx record.