Email Verifier - Email verifier app lets you verify email.
V12 Data - V12 Data offers rich data sets with verified addresses and emails for personalized marketing campaigns.
NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
Adobe Audience Manager - Adobe Audience Manager is a data management platform that integrates online and offline data to deliver a unified view of all your audiences
Email List Verify - The Fastest Way to Improve Email List Deliverability and ROI
Google Audience Center - 3 votes and 6 comments so far on Reddit