CampaignKit - Email Validation for marketers. Detect invalid and malicious email addresses in your email lists.
NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
Sender Policy Framework - This is a diagnostic tool that acts as a Sender Policy Framework (SPF) record lookup
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.