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.

Exim is described as 'Message transfer agent (MTA) developed at the University of Cambridge for use on Unix systems connected to the Internet' and is a Mail Server in the online services category. There are more than 10 alternatives to Exim for a variety of platforms, including Linux, Self-Hosted, BSD, Mac and Windows apps. The best Exim alternative is Postfix, which is both free and Open Source. Other great apps like Exim are Mail-in-a-box, KumoMTA, Haraka and OpenSMTPD.
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.


KumoMTA is the only true Open-Source PowerMTA alternative, capable of matching performance of several million messages per hour while providing granular traffic shaping configuration and automation across unlimited IPs.

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.

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.
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.




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An SMTP client that is extremely easy to configure and use, providing a simple HTTP API that is used for sending emails.