Postmark - Postmark is the easiest and most reliable way to be sure your important transactional emails get to the inbox. Simply & reliably parse recieved email to JSON for your webapp.
Yesmail - Yesmail provides email marketing solutions that integrate mobile, web, and social channels for marketers.
SendGrid - Learn why more developers choose SendGrid for their email deliverability service to send transactional emails triggered by web apps. Get started for free
PostageApp - PostageApp is an email management service that makes it easy to design, deliver, and manage all of the email that websites or applications send.
JangoSMTP - JangoSMTP is a transactional email delivery service that adds tracking and authentication to email.
Elastic Email - Elastic Email is an all-in-one email delivery platform for both marketing and transactional email.