Orphan email addresses

I have noticed that my database is full of email addresses that belonged mostly to deleted leads (also other beans such as accounts, contacts and users, but these are a minority).

In some cases these leads are no longer in the database and in other cases they are marked as deleted.

However the email addresses are still there and they are not marked as deleted.

Is there a way to purge them without having to go through them in the database one by one?

Wouldn’t it be a good idea that, when deleting something like a lead or a contact also the corresponding email (if not associated to other things) gets deleted too?