It would be nice if we could configure the default MX record(s) for the domain when editing domain templates. By default only one MX record is added:
domain.com. IN MX 5 mail.domain.com.
There should be an option to configure the default MX record(s) to use mail.domain.com, the server's hostname, or none, and maybe a textarea to add additional mail servers and priorities.
See attached screenshot for my idea of how this could work