MailChimp - MailChimp is the best way to design, send, and share email newsletters.
Lob - A simple API to integrate print & mail solutions into your applications.
Kingmailer - Kingmailer helps you send, receive and route/forward emails.
PostGrid - Transform your Offline Communications. Use our fully-documented REST API to send personalized letters, checks, postcards and improve address accuracy.
Awesome Mails - Awesome Mails creates beautiful image map emails, featuring an easy to use drag-and-drop editor...
AmazingMail - Business print-mail solution