NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
Roundcube - Web-based IMAP email client
Email List Verify - The Fastest Way to Improve Email List Deliverability and ROI
HEY - Email at its best, new from Basecamp.
clearout.io - Clearout Email Finder & Email Verification Service - Drive sustainable business growth by expanding your reach, lowering hard bounces, and improving deliverability rates.
Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.