Web hosting only domain configuration
If I setup a vsite that is only to be used for web hosting (where email is handled on a different server), I use the GUI to disable email for the domain and for any users. However, there are still some references to the domain within the sendmail config, leading the server to believe it is still authoritative for the domain. To fix this, I then have to edit /etc/mail/local-host-names and the virtusertable to remove the remaining references.
So, in addition to the present disable options, something like "Host email on this server" (default on) is needed, and when turned off, it remove every reference as listed earlier.