Gmail and other email services allow users to extend their address using the + (plus) character.
For example, mail to
will all be receivable by the owner of
In its default configuration, Drupal 7 would allow the owner of
email@example.com to register 3 separate accounts using the 3 addresses above... and more if they want!
I would like to prevent this type of multiple registration.
While I could just create a rule that blacklists email addresses containing the
+ character, there are legitimate uses of this.
I would prefer to be able to check for other equivalent email addresses, where in the above example, all 3 addresses are equivalent, because they are all collectable by
firstname.lastname@example.org, and allow only one of them.
Is there some way to do that?