quan_flo

If there is a user (or a bot) that signed up at your site this user can start to send messages to every other user. 
I had some negative experiences with this and so I wrote a module that should help to block such a spam.
Buddypress Messages Spam Blocker introduces some restrictions to your users:
<ul>
<li>New users can send messages only 24h after their registration, so you’ll have time if bot registrations have to be removed manually (modify this value using filter ‘buddypress_messages_spamblocker_newMembersWaitingPeriod’)</li>
</ul>
Their are also some more restrictions for mass mailings (mails that are sent to “friends” of the contact list are not included in this calculation):
<ul>
<li>Users can send 6 messages maximum in 5 minutes (modify this value using filter ‘buddypress_messages_spamblocker_5m’)</li>
<li>Users can send 10 messages maximum in 10 minutes (modify this value using filter ‘buddypress_messages_spamblocker_10m’)</li>
<li>Users can send 20 messages maximum in 30 minutes (modify this value using filter ‘buddypress_messages_spamblocker_30m’)</li>
<li>Users can send 30 messages maximum in 60 minutes (modify this value using filter ‘buddypress_messages_spamblocker_60m’)</li>
<li>Users can send 35 messages maximum in 12 hours (modify this value using filter ‘buddypress_messages_spamblocker_12h’)</li>
<li>Users can send 45 messages maximum in 24 hours (modify this value using filter ‘buddypress_messages_spamblocker_24h’)</li>
<li>Users can send 50 messages maximum in 48 hours (modify this value using filter ‘buddypress_messages_spamblocker_48h’)</li>
</ul>
Users with the capability “edit_users” (admins etc.) have no restrictions for outgoing messages
Install, activate, and it will work.
More about me and my plugins
Since the year 1999 I do administration, customizing and programming for several forums, communities and social networks. In the year 2013 I switched from another PHP framework to WordPress. 
Because not all plugins I’d like to have exist already I wrote some own plugins and I think I’ll continue to do so.
If you have the scope at forums or social networks my other modules might also be interesting for you. <a href="https://wordpress.org/plugins/search.php?q=quan_flo" title="ifs-net / quan_flo WordPress Plugins" rel="ugc">Just take a look at my WordPress Profile to see all my Plugins.</a> Use them and if my work helps you to save time, earn money or just makes you happy feel free to donate – Thanks. The donation link can be found at the right sidebar next to this text.

Buddypress Messages Spam Blocker

This plugin will block mass mailing for the buddypress messaging system

Yehi

Wiliba

Advanced Notifications allows you to create beautiful custom notifications that appear on pages or posts of your choice.
Demos – <a href="https://advanced-notifications.com/demos/" rel="nofollow ugc">Advanced Notifications – Live Preview</a>
<h4>In development:</h4>
<ul>
<li>More designs</li>
<li>More animations</li>
</ul>
<h4>Features:</h4>
Here’s a list of the Basic version features in plain text format:
Notifications
<ul>
<li>Number of Notifications: Unlimited</li>
<li>Types: Editor, Image, HTML</li>
<li>Notification by User Role Types: Always all users & visitors, All users & visitors</li>
<li>Scheduled Notification: No</li>
<li>Notification by Devices Types: All devices, Desktop, Desktop & Tablet, Tablet, Only Tablet & Mobile, Mobile</li>
<li>Delay Before Show: Yes</li>
<li>Show Time: Yes</li>
<li>Publish Type: All site pages, Custom post types & taxonomies, Only on specific pages</li>
<li>Limiting the Number of Shows per Period: Yes</li>
<li>Animations In & Out: Basic</li>
<li>APIs for Developers: Yes</li>
</ul>
Locations
<ul>
<li>Number of Locations: Unlimited</li>
<li>Locations: Bottom & Left, Bottom & Right, Top & Left, Top & Right</li>
<li>Custom Location Options: Basic</li>
<li>Responsive: Yes</li>
</ul>
Designs
<ul>
<li>Number of Designs: Unlimited</li>
<li>Designs: Default, Success, Info, Warning</li>
<li>Custom Design Options: Basic</li>
<li>Responsive: Yes</li>
</ul>
Triggers
<ul>
<li>Number of Triggers: Unlimited</li>
<li>Number of Triggers per Notification: Only one</li>
<li>Notifications Mode: Page is loaded and in triggers</li>
<li>Triggers: Mouse leave from top, On click, On hover</li>
<li>Trigger Action: Only show notification</li>
</ul>
Full Features – <a href="https://advanced-notifications.com/features/" rel="nofollow ugc">Advanced Notifications – Features</a>
<h4>Feedback</h4>
If you like this plugin, then please leave us a good rating and review. 
<a href="https://wordpress.org/support/plugin/advanced-notifications/reviews/" rel="ugc">Advanced Notifications – Reviews</a>

Advanced Notifications

Advanced Notifications allows you to create beautiful custom notifications that appear on pages or posts of your choice.

Buddypress Messages Spam Blocker vs Advanced Notifications