Halon MTA - Scriptable and scalable SMTP server and email framework designed for service providers.

Email Inspire - Discover the best of email design and marketing — Browse email newsletters from top brands.

KumoMTA - KumoMTA is the world's first Open-Source MTA designed from the ground-up for large-volume senders. Get a fast, flexible, supported solution.

EmailWay - Collection of the most insightful and informative email newsletters from across a wide spectrum of industries and interests

MailerQ - MailerQ is a high performance Mail Transfer Agent (MTA) designed for delivering large volume email messages at very high speeds.

Really Good Emails - A large collection of good product email design.