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

Edward

Site Announcements allows you to broadcast site-wide messages to your visitors, as well as set custom parameters for the messages, 
such as the background and text color, and how long a user-hidden announcement should be hidden from users.
By default, announcements will open in a slide-down modal (showing the announcement content). Alternatively, each announcement can be configured to point to an internal or external URL. Announcements with no URL and no content will simply display user-selected text, which can be handy for broadcasting things like coupon codes or important messages to users.
Plays well with the WordPress Admin Toolbar and is mobile-friendly. Has been tested with 100+ WordPress themes and should work well on all themes. If you have theme compatibility issues, please post a support thread or contact me.
The plugin’s font sizes and families are inherited from the theme. If you wish to make adjustments to the announcement bar’s font sizes or types you will need to add custom CSS to override your theme’s styles.
Site Announcements uses animate.css for the modal transitions and JSCookie for setting a cookie if a user hides a modal.

Site Announcements

Site Announcements allows you to broadcast site-wide messages to your visitors, as well as set custom parameters for the messages, such as the backgro …

Buddypress Messages Spam Blocker vs Site Announcements