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.

alexhal

Allows Buddypress group Mods to send email to all group members from group admin/manage section. 
To enable E-mail members for mods simply put the code given below in your bp-groups-members-mail.php file in the end from wp-admin-> plugins-> editor :
<pre><code>add_filter('gmm_enable_for_mods','gmm_enabled_for_mods');
function gmm_enabled_for_mods(){
 return true;
}
</code></pre>
By default this “E-Mail Members” section is available to mods and admin . 
To change it a filter is available and you can change the access like this : 
To restrict this option to admins only 
 add_filter(‘bp_gmm_auhority’,function(){ 
 return ‘admin’; 
 });

Group Members Mail Plugin

I've done a quick test and it worked with no problems for unformatted email

Does what it says on the tin!

Allows Buddypress group Mods to send email to all group members .

Email All Users vs Group Members Mail Plugin