Looking to limit PM communication between users based on their user group. More specifically:
Vbulletin control panel -> Usergroup manager -> Private Message Permission
Should get another option: PM Communication Allowed with usergroups and the field for usergroup ids that this group is allowed to communicate with
Example: usergroup private is allowed to PM only to usergroup sergeants;
usergroup sergeants is able to PM to privates and lieutenants… etc
Finally, warning message should show up when someone tries to PM to unauthorized group: Based on your rank you are authorized to PM only to group1, group2, …
In case of success will provide with several other vbulletin related projects.