When I was running ~20 domains on a Zimbra server I had every domain setup with mail.company.com as it's MX record and the PTR record said xxx.xxx.xxx.xxx IP address was mail.company.com
So as an example:
The MX record for freecheese.com was "0 mail.company.com"
mail.freecheese.com was a valid dns entry that pointed to the IP address of the Zimbra server, and mail.freecheese.com was also setup as a virtual host in Zimbra, so users of that domain would have no idea they were actually using mail.company.com unless they looked at the MX record for their domain. The PTR record of the IP address pointed to mail.company.com. |