Trumail - Free email verification API
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!
Email List Verify - The Fastest Way to Improve Email List Deliverability and ROI
Proofy - Quickly validate and verify your email lists.
ZeroBounce - Removes invalid emails from your list to prevent email bounces from ruining your deliverability.
NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.