Admin has the ability to block PMs from any user. That seldom happens but when a user keeps filling our mailbox with PMs and will not stop we may block them so that we can get our other work done.
Users who simply want to argue may get blocked.
Users who attack me and call me vulgar names will get blocked or booted.
If we have a user blocked we still have the ability to send them PM warnings etc.
If you saw some of the PMs that arrive in our mailboxes you would understand why we have it set up this way.