We have successfully implemented a Block List into our Private Messenger (PM) Service where registered users can choose which other registered users to block. It is very simple to use - simply enter the userID of a registered user and click “Block”. Likewise, you can “Unblock” any blocked registered users whenever you wish. For unregistered users, we decided that the best way to do it is to “Block or Unblock all unregistered users” at once. Since it is almost impossible to know who the unregistered users are as individuals, we have no choice but to implement our Block List in this way.
Below is a screenshot of the Block List page under “My Messages“: