Apility.io - Threat Intelligence Anti Abuse API to find out in advance if your users will be good customers. Learn if your users are on an abuse blacklist and decide how to proceed.
Email Checker - Email Checker offers a real-time API and bulk validation for list cleaning.
TrueMail.io - TrueMail.io is an email checker service.
Atomic Mail Verifier - Email Verifier offers a comprehensive three-step verification process designed to help you identify and eliminate a significant number of non-existent email addresses.
Simple Email Verifier - Simple email verifier is PHP script use Trumail API to verify bulk email addresses.
ZeroBounce - Removes invalid emails from your list to prevent email bounces from ruining your deliverability.