NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
Antideo Email Validator - Antideo Email Validation plugin for WordPress ensures that you get to validate emails in real time
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MailRefine - Decrease Email Bouncing With Best Email Verifier
Verimail - Clean up email-address lists of any size or use our powerful API for real-time verification.
CampaignKit - Email Validation for marketers. Detect invalid and malicious email addresses in your email lists.