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Create groups to organize your subscribed users and send them e-mails based on their groups or by user levels, capabilities or usernames. You can also send messages for anybody, directly by e-mail addresses. Besides that, you can use some information of the current user and of a selected publication (post or page), to personalize the message, that can take attached files, if you want. WPMailing offers support if you are using Xinha4WP or Dean’s FCKEditor, to write e-mails in your favorite editor.
<h3>Features</h3>
Once the plugin is activated, your administration panels will offer:
<ul>
<li>The ability to create groups and tag your users, by adding new features in Users section pages 
through Javascript (user.php, profile.php and user-edit.php). 
** This actions will not modify the WP original files.</li>
<li>An interface to modify names and descriptions of your groups (Manage > Groups) </li>
<li>An interface to compose and send e-mails to subscribed users, 
with some interesting features (Write > Write e-mail): 
** The ‘To’ field supports multiple e-mails and inclusions by user level, capability, group or username. 
** You can attach multiple files to the message 
** You can use values of an specific post or page 
** The e-mail can be personalized with informations of the user that will receive the message</li>
<li>An interface to set or update some WPMailing configurations (Options > Mailing) </li>
<li>Complete information about the sending process after you send any e-mail</li>
</ul>
<h3>Feedback</h3>
Your feedback are welcome. 
 Send any bug detections, suggestions, critics, etc. to: wpmailing(at)jsbrasil(dot)com 
 Thank you, Cau Guanabara.

WPMailing

Create groups to organize your subscribed users and send them e-mails based on their groups or by user levels, capabilities or usernames.

itthinx

This plugin redirects 404’s caused by hits on pages that are protected by <a href="https://wordpress.org/plugins/groups/" rel="ugc">Groups</a>.
The redirection settings can be adjusted in Settings > Groups 404 :
Visits to protected pages can be redirected to:
<ul>
<li>a specific post, or</li>
<li>the WordPress login</li>
</ul>
The redirection can also be applied for restricted categories, tags and other taxonomy terms if <a href="https://www.itthinx.com/shop/groups-restrict-categories/" rel="nofollow ugc">Groups Restrict Categories</a> is used.
The redirect status code can be selected among:
<ul>
<li>Moved Permanently (301)</li>
<li>Found (302)</li>
<li>See other (303)</li>
<li>Temporary Redirect (307)</li>
</ul>

Groups 404 Redirect

I know this plugin hasn't been updated in a couple years, but IMHO Groups and its related plugins (like this one) are a hidden gem for WordPress sites. So many people jump to complicated membership plugins when they could do everything they need with Groups. This 404 redirect add-on works like a charm. I'm using it on the latest version of WP 5.x

Perfect.

Redirect 404's when a visitor tries to access a page protected by Groups.

WPMailing vs Groups 404 Redirect