The only option I can find is to stop them from starting a personal conversation. The only option I can find that blocks use of the PM system is to "never" the view permission, but this trashes use of the whole forum too.
The background to this is either users who abuse the PM system, or, users who do not update their registered emails and I get bounced notifications. In these cases I would like to suspend the messaging system until they update their email.
It would be good to find a way that a user can have the "no permission" response when trying to access the message system and an error generated when another member tries to PM them (eg "That user is blocked from using the PM system").
Any suggestions please?