Restrict people sending random (possibly abusive) messages to others before get accepted as friend
Currently any user can send message (sometimes abusive message which can be a harassment) to any other user without actually be part of her/his group of friends. The recipient can then block and delete the sender from his/ her list. This sometimes is too late and damage has already been done.
For the first contact, the only possible message should be a request for friendship created automatically by the program to avoid possible abuse.
Which protocol? Maybe existing StopSpam plugin would be helpful for you.