Email List Verify - The Fastest Way to Improve Email List Deliverability and ROI
Bulk Email Verifier - Clean up your large mailing lists before you use them. Clean list increases your reputation in MailChimp, AWeber, or Campayn.
NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
Email Verifier - Email verifier app lets you verify email.
MailboxValidator - MailboxValidator - Verify Email Address
Email Verification on Google Sheets - An add-on for email verification directly in Google Sheets