r-a-y

By default, any member on your BuddyPress site is allowed to send private messages to anyone in your userbase.
This plugin only allows friends and site administrators to send private messages. Thus, acting as another deterrent from illegitimate users.
<h3>Donate!</h3>
I’m a forum moderator on the buddypress.org forums. I spend a lot of my free time helping people – pro bono!
If you downloaded this plugin and like it, please:
<ul>
<li><a href="https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=CT8KZGFEVA3R6" rel="nofollow ugc">Fund my work soundtrack!</a> Music helps me help you! A dollar lets me buy a new tune off Amazon MP3, Amie Street or emusic.com! Or if you’re feeling generous, you can help me buy a whole CD! If you choose to donate, let me know what songs or which CD you want me to listen to! 🙂</li>
<li>Rate this plugin</li>
<li>Spread the gospel of BuddyPress</li>
</ul>

BuddyPress Private Messages for Friends Only

This plugin only allows friends and site administrators to send private messages on your BuddyPress site.

Shamim Hasan

Front End PM extension to integrate with Ultimate Member. This works out of the box, no settings required.
<a href="https://wordpress.org/plugins/front-end-pm/" rel="ugc">Front End PM</a> 
<a href="https://wordpress.org/plugins/ultimate-member/" rel="ugc">Ultimate Member – User Profile & Membership Plugin</a>
This two plugins need to be activated first before activating this extension.
Once activated, you will see “Message” Tab in user profile and account page. If it is own profile then clicking “Message” will show full message system, if it is another user profile then clicking “Message” will show a form which will send message directly to that user.
<a href="https://www.shamimsplugins.com/docs/front-end-pm/integration/front-end-pm-ultimate-member-integration/?utm_campaign=wordpress&utm_source=readme&utm_medium=description" rel="nofollow ugc">More Details</a>
Github
<a href="https://github.com/shamim2883/front-end-pm-ultimate-member-integration" rel="nofollow ugc">https://github.com/shamim2883/front-end-pm-ultimate-member-integration</a>

Front End PM – Ultimate Member Integration

Very much useful extension

Front End PM extension to integrate with Ultimate Member

BuddyPress Private Messages for Friends Only vs Front End PM – Ultimate Member Integration