NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
CampaignKit - Email Validation for marketers. Detect invalid and malicious email addresses in your email lists.
Email Verifier - Email verifier app lets you verify email.
Sender Policy Framework - This is a diagnostic tool that acts as a Sender Policy Framework (SPF) record lookup
Verimail - Clean up email-address lists of any size or use our powerful API for real-time verification.
MailRefine - Decrease Email Bouncing With Best Email Verifier