GMass - GMass allows you to easily schedule emails, send out mass emails and mail merge campaigns and more with Gmail! Click here to learn about more features!
Bouncebuster by Overloop - Bouncebuster is a real-time email verifier that helps you fight bounce & increase email deliverability.
Trumail - Free email verification API
Free Email Verifier - The first free and accurate email verification service
ZeroBounce - Removes invalid emails from your list to prevent email bounces from ruining your deliverability.
The Ultimate Google Sheet Toolkit - We put together a curated list of templates, videos, and tutorials that can help you build your analytics expertise.