CampaignKit - Email Validation for marketers. Detect invalid and malicious email addresses in your email lists.
TrueMail.io - TrueMail.io is an email checker service.
Null Bounce - Null Bounce is an email validation tool that helps companies decrease the bounce rate for email campaigns. Also, the service is available as an API, which can be used, for example, on sign-up forms to ensure that user submits a valid email address.
TheChecker.co - Accurate email verification at low prices.
Captain Verify - Captain Verify is the best solution to Verify & Clean the validity of your emails.
Verimail - Clean up email-address lists of any size or use our powerful API for real-time verification.