ZeroBounce - Removes invalid emails from your list to prevent email bounces from ruining your deliverability.
Proofy - Quickly validate and verify your email lists.
Email Checker - Email Checker offers a real-time API and bulk validation for list cleaning.
Trumail - Free email verification API
Bulk Email Checker - Bulk Email Checker is an online service used to Verify and Clean Email Addresses. Its Easy to Use, Reliable and used by 1000's of Businesses.
Email Hippo - Email Hippo provides online email validation service for professional marketers and their clients.