Arefly

Check if the Email’s Gravatar is exist.
檢測指定郵箱的Gravatar是否存在
Example:
<pre><code>if(validate_gravatar("name@domain.com")){
 echo "This Email have Gravatar!";
}else{
 echo "This Email do not have Gravatar!";
}
</code></pre>

Validate Gravatar

Check if the Email's Gravatar is exist. 檢測指定郵箱的Gravatar是否存在

adaptsites

Kegan Quimby

This plugin adds filters to the WordPress user registration process. It lets you check user signups against StopForumSpam.com and/or Emailable.com
When a user registers, you can configure this plugin to use the submitted email address and IP address to first check against StopForumSpam.com to see if there is a match to the IP address and/or the email address in their FREE database. Then you can check if the ending of the email address is .ru or another country extension you want to block to cut down on spam registrations. Finally, if it passes these checks, you can check the email address against Emailable.com to see if the email is valid.
<a href="https://emailable.com" rel="nofollow ugc">Emailable.com</a> 
Validate user registration emails using Emailable.com to see if an email is: deliverable, risky, unknown, or undeliverable.

Add Spam Filters

Stop Spam User Registrations by Adding StopForumSpam.com, Emailable.com, and Email Domain Extension Filters.

Validate Gravatar vs Add Spam Filters