please follow-up on the mailing list (Cc:-ed) so others can answer and learn
Jan Beerden wrote:
We already tried that. We are trying to prevent user1 to have an
that is the same as user2's primary email address.
What we would like is that a certain value (email address) has to be unique
across both the email and the alias attribute.
Uniqueness is only per attribute. So this is not possible.