NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
ZeroBounce - Removes invalid emails from your list to prevent email bounces from ruining your deliverability.
Email List Verify - The Fastest Way to Improve Email List Deliverability and ROI
TheChecker.co - Accurate email verification at low prices.
Proofy - Quickly validate and verify your email lists.
Bulk Email Verifier - Clean up your large mailing lists before you use them. Clean list increases your reputation in MailChimp, AWeber, or Campayn.