Example: In the KB on phpbb 3 it says
Group able to receive private messages
This will allow the sending of Private Messages to this group. Please note, that it can be dangerous to allow this for Registered Users, for instance. There is no permission to deny the sending to groups, so anyone who is able to send Private Messages will be able to send a message to this group!
However, there are options that DISALLOW sending messages to groups on a group by group basis. If I mark a group NO they cannot send group messages, but then mark the group itself YES they can get messages - which overrides which?
What if someone is in 2 groups? Group 1 is ALLOWED and group 2 is not allowed.... which permission overrides the other?