Block users from re-using old password, especially for mailboxes
System could remember a certain number of old passwords (admin configurable) and prevent user from selecting these again.
Have had more cases than I'd like to admit where customer re-used a previously compromised password. If Plesk remembered the last x passwords used by that account it would help.
Also adding ability so Plesk checks a server configurable password blacklist before accepting customers new selection would be appreciated.