Reject School Domain Email Address on Multiple Profiles

We recently accepted a student whose email address using our default nomenclature (FirstinitialLastname) happened to be the same as for an existing student. Our IT person didn't notice this at the time, so we had two students with the same system email address for about a day. One way to reduce the likelihood of similar situations would be for us to use a more complex naming system, but it would also be helpful if Populi could automatically reject any email address in the school domain being added to a second profile. We wouldn't worry about this for external emails (such as a husband and wife sharing a Gmail account), just for the ones we create and assign.