[Req]No PMs allowed if members in the same user group

[mr9x]

Hi,
I need to prevent my users from sending private messages to other users in the same user group (if the sender/receiver in the same user group).
Example: if you are in group1, you cannot send messages to another user in group1, but you can send messages to users in group2 or group3, etc.

I'm willing to pay for this modification.