NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
Email List Verify - The Fastest Way to Improve Email List Deliverability and ROI
Verimail - Clean up email-address lists of any size or use our powerful API for real-time verification.
ZeroBounce - Removes invalid emails from your list to prevent email bounces from ruining your deliverability.
Email Verifier - Email verifier app lets you verify email.
Reacher - Check if an email exists without sending any email.