PostGrid has been great for automating our insurance mails for our client
AuthSMTP - AuthSMTP is the outgoing SMTP email service for e-commerce websites, mailing lists or email applications.
Lob - A simple API to integrate print & mail solutions into your applications.
BriteVerify - Email Validation & Email Verification reduces bounce rates up to 98%. Rapidly verifying email addresses has never been easier, just drag drop and deliver!
Postalytics - Automated direct mail software that’s faster, smarter & better. Postalytics sends personalized direct mail from your CRM and analyzes delivery & response.
CritSend - CritSend is a SMTP relay for developers.
AmazingMail - Business print-mail solution