ElbowRobo

This plugin is for BuddyPress, it adds a dashboard menu and a tab in the messages section. Once you navigate into the messages section and click the “Mass Messaging” tab you have access to all the options which you chose in the dashboard.
Including mass messaging to:
<ul>
<li>Members</li>
<li>Members of Groups</li>
<li>Members of Blogs (Sites)</li>
</ul>
And:
<ul>
<li>Select all buttons to allow mass messaging to all members easily.</li>
</ul>
In this page you also see ‘subject’ and ‘description’ just like on the Buddypress compose page.

Mass Messaging in BuddyPress

This works great for what I need, thanks a lot!

Great plugin

Ever wanted to send a message to many people at once? Now you can, introducing - Mass Messaging.

Zodor

Email All Users is a plugin that creates a widget that allows you to send mass email to all registered users in your wordpress site. 
You configure the widget with a title and mailto-link-title. 
The widget will then create a mailto:link that will include all users that is active. 
If you have the plugin “Email Users” installed it will only include users that has approved mass email in the settings.

Email All Users

Email All Users is a plugin that allows you to send mass email to all registered users in your wordpress site.

Mass Messaging in BuddyPress vs Email All Users