This is great, thanks for your effort. Couple more things I'd love to see:

1. Parse a chunk of text and salvage any email addresses from it that you can find. Use case: my users upload spreadhseets with email of their other team members, but email field would often contain more than one email (separated by slash or space or coma or god knows what), or other stuff like Skype account etc.

2. Actual validation service. I'd pay for it at standard mailgun rates, it would be easier for me than rolling my own as I do now.

Thanks again!