TrueMail.io - TrueMail.io is an email checker service.
NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
TheChecker.co - Accurate email verification at low prices.
ZeroBounce - Removes invalid emails from your list to prevent email bounces from ruining your deliverability.
DeBounce - Email Validation, Email Checker, Data Enrichment and Appending Tool. Using DeBounce remove invalid, disposable, spam-trap, syntax and deactivated emails.
clearout.io - The easiest and real-time email verification and validation tool.