So here is my scenario, I want to setup Zimbra Network Edition so that it will host multiple domains. This isn't a problem, I can do this. But what I want is for the hostname of the server to be different from any of the domains that I will be setting up. I will not be using bind, as I have access to setup all the domains MX, etc records externally and then perform the necessary forwarding at my SonicWall to the email server for all the domains. Do I have to have the hostname resolve MX records properly as well, or just the domains that I want to setup.
The reason I am asking is because I will ultimately have 2 email servers setup, the first one is already going and has been for the last year (no problems there), lets call it mail.example.com, and now I have been mandated to setup a second email server for "sister" companies and I would like the host to be mail2.example.com. Two completely different email servers, the first email server will host example.com and the second will host example1.com, example2.com, etc.
Does this make sense and can I do what I want to do? Or does the second email server have to have a different hostname all together. So instead of having the first email server being mail.example.com and the second being mail2.example.com, does the second have to be something like mail.example2.com.

Please note that I have the domains already that I want to setup so that is not an issue.

Any help would be great.