The banned emails list is no emptied

Hello.

When I ban a member, I also ban his email if he wants to unsuscribe by himself ; like that he can't register with the same email address.
But this list seems to be cleared every month, just like the list of banned IP address.
I suggest that the banned emails list isn't cleared every month.

PS : Thanks Cornelia for helping me to translate

This would be help full I vote yes.