Courier-MTA is described as 'The Courier mail transfer agent (MTA) is an integrated mail/groupware server based on open commodity protocols, such as ESMTP, IMAP, POP3, LDAP, SSL, and HTTP. Courier provides ESMTP, IMAP, POP3, webmail, and mailing list services within a single, consistent, framework' and is a Mail Server in the office & productivity category. There are more than 10 alternatives to Courier-MTA for a variety of platforms, including Linux, Mac, Windows, BSD and Self-Hosted apps. The best Courier-MTA alternative is Postfix, which is both free and Open Source. Other great apps like Courier-MTA are Mail-in-a-box, Exim, OpenSMTPD and Sendmail.
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.
Mail-in-a-box is not an MTA, but a tool to deploy an MTA on a “cloud” server, that happens to include an MTA. It is like the difference between a rocket and a launchpad that happens to come with a rocket. You get an easieer deployment, at the cost of not being able to choose the MTA anymore. It is the age old stroy of trading freedom for convenience.
Exim is a message transfer agent (MTA) developed at the University of Cambridge for use on Unix systems connected to the Internet.
OpenSMTPD is a FREE implementation of the server-side SMTP protocol as defined by RFC 5321, with some additional standard extensions. It allows ordinary machines to exchange e-mails with other systems speaking the SMTP protocol.
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.
sSMTP is a simple MTA to deliver mail from a computer to a mail server. sSMTP is simple and lightweight, there are no daemons or anything hogging up CPU; Just sSMTP. Unlike Exim4, sSMTP does not receive mail, expand aliases, or manage a queue.
A small Mail Transport Agent (MTA), designed for home and office use. Part of DragonFly BSD , it accepts mails from locally installed Mail User Agents (MUA) and delivers the mails either locally or to a remote destination.
Configure SMTP e-mail in IIS when you want to deliver e-mail messages from your site. Mail can be delivered immediately or it can be delivered to a file location on disk where it can be retrieved for delivery later.
An SMTP client that is extremely easy to configure and use, providing a simple HTTP API that is used for sending emails.
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.
EmailSuccess, an advanced SMTP Server (MTA) built from the ground up to handle the most critical reliability, performance, security, and deliverability requirements.
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Versatile and modular. Lets you combine things the way you want. Decades of being honed by real-world usage. Does not make you feel limited by what the develepers deemed suitable for you.