With BP Private community Pro plugin allows you to restrict the user roles from sending a new message, from sending replies, from starting messages to multiple friends, Prevent messaging from nonfriends, etc.
WB Plugins >> Community Pro>> Membership Restrictions, And select the user role from the dropdown.
Scroll down and open the tab Messages Restrictions, and access the following settings
- Prevent Role From Starting a New Conversation.
- Prevent Role From Sending Messages Replies.
- Prevent Role From Starting a Multiple Conversation.
- Prevent Messaging Non-Friends: User Can’t message non-friends users.
- Max Messaged Users: How many users can this role message?
- Max Messages Per Account: How many messages can this role send per account?