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 List Verify - The Fastest Way to Improve Email List Deliverability and ROI
TrueMail.io - TrueMail.io is an email checker service.
NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
Simple Email Verifier - Simple email verifier is PHP script use Trumail API to verify bulk email addresses.
Email Verifier - Email verifier app lets you verify email.