Proofy - Quickly validate and verify your email lists.
Two Factor Auth (2FA) - List of websites and whether or not they support 2FA
Trumail - Free email verification API
X (Twitter) - Connect with your friends and other fascinating people. Get in-the-moment updates on the things that interest you. And watch events unfold, in real time, from every angle.
Email List Verify - The Fastest Way to Improve Email List Deliverability and ROI
Rapid 2FA - A painless way to add two-factor authentication to your site