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
Email List Verify - The Fastest Way to Improve Email List Deliverability and ROI
MailRefine - Decrease Email Bouncing With Best Email Verifier
DeBounce - Email Validation, Email Checker, Data Enrichment and Appending Tool. Using DeBounce remove invalid, disposable, spam-trap, syntax and deactivated emails.
CampaignKit - Email Validation for marketers. Detect invalid and malicious email addresses in your email lists.