Joel

User Spam Remover is a plugin for WordPress that automatically removes spam user registrations and other old, never-used user accounts. It also blocks the notification e-mail that WordPress normally sends to the administrator whenever a new user registers (annoying when that registration is spam!) and logs it instead.
The plugin adds a configuration panel so that all of these options can be turned on or off, and it logs and fully backs up all user accounts that it deletes, so that you can restore them if you need to.
Features:
<ul>
<li>
Automatically deletes user registration spam and other orphaned, never-used accounts.
</li>
<li>
Very simple, enable and go! Doesn’t interfere with the normal user registration process in any way. So, it doesn’t add captchas or activation or anything else — you’re free to use it alongside a plugin that does, if you like.
</li>
<li>
Blocks notification e-mail that WordPress normally sends to the administrator every time a new user registers (instead, logs this event).
</li>
<li>
Fully configurable, with grace period for new accounts and optional username whitelist.
</li>
<li>
Fully logs all actions and backs up all user accounts that it deletes so that you can seamlessly restore them if you ever need to.
</li>
</ul>
Please see requirements and installation instructions below, or online <a href="https://wordpress.org/support/topic/official-installation-instructions-and-what-to-do-about-errors/" rel="ugc">in the WordPress support forum</a>.
For more information, please go to: <a href="https://lyncd.com/user-spam-remover/" rel="nofollow ugc">https://lyncd.com/user-spam-remover/</a>

User Spam Remover

Great way to clean a long running site of "junk" users.

Removed over 29k in minutes..

Effective

Does not work with many WordPress sites throwing a fatal error about mysqli.

Fatal PHP error about mysqli on activation

I had 31000 subscribers on a old (WP 4.4) website where I accidentially had the option "anyone can register" turned on.
This plugin did the job of deleting all those subscribers. I had to do it in batches as it "only" deletes 1000 subs at the time.

Thanks a lot to the developer as it has saved me a lot of hassle!!

It works!

Automatically removes spam user registrations and other old, unused user accounts. Blocks annoying e-mail to administrator after new registrations.

Benaceur

This plugin allows you to Restrict a particular or certain username, email addresses or symbols, 
or email from specific domain names in the form registration when registering for your site 
and you can allow to use a certain language (arabic cyrillic latin …) 
or all languages and characters and symbols, you can also control and modify all errors messages 
and allow certain characters (Symbols and characters accented as é û), 
and allowing you to change the author slug (defaults to the username of the author), 
and you can control and adjust all settings from the plugin settings page in admin Panel.
<h4>and here is all plugin settings in admin Panel:</h4>
<ul>
<li>enable/disable the plugin</li>
<li>disallow to use the spaces in username</li>
<li>disallow to use only numbers in username</li>
<li>disallow all characters (Symbols) in username</li>
<li>disallow characters (Symbols) permitted by wordpress in username: @ – . _</li>
<li>allow certain characters (Symbols and characters accented as é û)</li>
<li>restrict certain email addresses</li>
<li>restrict certain username</li>
<li>restrict certain domain names for example: yournamesite@com</li>
<li>No/yes uppercase in username</li>
<li>Compatible with single site, network (multi-site), buddypress and buddyboss.</li>
<li>The possibility to:</li>
<li>choose language (characters) in username (arabic cyrillic latin …) or all languages</li>
<li>remove all settings and data of the plugin from database when the plugin is disabled</li>
<li>reset default settings</li>
<li>control and modify all errors messages</li>
<li>restrict any name contains a part of word (partial matching)</li>
<li>prevent the use of email in the username</li>
<li>prevent the use of numbers more than letters and symbols in the user name.</li>
<li>allowing you to change the author slug</li>
<li>Author Slug Structure</li>
<li>Update of the author’s slug for all users</li>
<li>Limit the number of users to update (in batches) with every click, if your database is big</li>
<li>Update or convert only names (author slug) not latin</li>
<li>remove name field in buddypress.</li>
<li>hide or change message (Must be at least 4 characters, letters and numbers only.) of multisite.</li>
<li>add an notice or text in registration form.</li>
<li>etc…</li>
</ul>
<h4>TRANSLATED IN FOLLOWING LANGUAGES:</h4>
<ul>
<li>Arabic</li>
<li>English</li>
</ul>
<h4>Direct support page:</h4>
https://benaceur-php.com/?p=2268

Restrict Usernames Emails Characters

Restrict the usernames, email addresses, characters and symbols or email from specific domain names or language in registration ...

User Spam Remover vs Restrict Usernames Emails Characters