PostGrid has been great for automating our insurance mails for our client
SendGrid - Learn why more developers choose SendGrid for their email deliverability service to send transactional emails triggered by web apps. Get started for free
Lob - A simple API to integrate print & mail solutions into your applications.
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.
Postalytics - Automated direct mail software that’s faster, smarter & better. Postalytics sends personalized direct mail from your CRM and analyzes delivery & response.
JangoSMTP - JangoSMTP is a transactional email delivery service that adds tracking and authentication to email.
Growmail Automated Direct Mail - Growmail enables businesses to send letters and postcards instantly through Automated Direct Mail.