In our extranet, a lot of users have been created multiple times with different usernames - which leads to unnecessary license consumption and confusion when assigning user permissions.

If we had the possibility to set a field validation to “e-mail address” (@.*), a large part of these duplicates could be prevented at the time of creation. This would save a lot of time for cleaning up these duplicates and also license costs.

An optional validation (e.g. based on a regex string that can be maintained in /admin) would create a real benefit.