Globally require unique emails

[rubberducky]

So right now I have a few clients who have one office email, but multiple user accounts to the pbx.
For instance:

Username - Email
fred - office@example.com
bob - office@example.com
susie - office@example.com

Is there a way to either require unique emails, or give a warning when a duplicate email is detected?

 

[Adrian Fretwell]

The simplest thing may be to put a unique constraint on the DB table column.