MailerQ is described as 'high performance Mail Transfer Agent (MTA) and a very fast SMTP server, designed to deliver large volumes of email messages at very high speeds. MailerQ is based on RabbitMQ AMQP'. There are seven alternatives to MailerQ for a variety of platforms, including Linux, Mac, Self-Hosted solutions, Java and Windows. The best alternative is Postfix, which is both free and Open Source. Other great apps like MailerQ are Sendmail (Free, Open Source), Exim (Free, Open Source), PowerMTA (Paid) and EmailSuccess (Paid).
Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail. It attempts to be fast, easy to administer, and secure. The software is also known by its former names VMailer and IBM Secure Mailer.
Sendmail is a general purpose internetwork email routing facility that supports many kinds of transfer and delivery methods, including the Simple Mail Transfer Protocol (SMTP) used for email transport over the Internet.
Email gateway application (SMTP server) that makes it easy for senders to adopt the latest authentication specifications ( SPF and DKIM) to comply with changing ISP policies for accountable outbound email delivery. No over hype. It just delivers.
NikaMail is a portable, extendable, zero-config email server. It is designed to perform automation tasks, provide access to mailboxes (port 110), serve as a mail transfer agent (port 587) and mail exchange service (port 25). NikaMail supports TLS.