Courier-MTA!

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. A descendant of the delivermail program written by Eric Allman, Sendmail is a well-known project of the free and open source software and Unix communities, and has spread both as free software and proprietary software.

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. Remote delivery includes several features like TLS/SSL support and SMTP authentication. dma is not intended as a replacement for real, big MTAs like Sendmail or Postfix. Consequently, dma does not listen on port 25 for incoming connections. »

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.

Available in Windows and Windows Server via the optional IIS role.

PowerMTA is an “enterprise” grade infrastructure application for email built to address the challenges of critical digital messaging environments and customer communications. PowerMTA™ is (advanced smtp software) providing unsurpassed reliability and delivery execution, with granular connection controls. Offering superior message throughput, simplified set up and configuration, and visibility through real-time reporting and tracking, PowerMTA™ pays dividends immediately. It is built on advanced multi-threaded persistent architecture—for messaging breakthrough that delivers unsurpassed resilience and performance. »

SSMTP is a program which delivers email from a local computer to a configured mailhost (mailhub). It is not a mail server (like feature-rich mail server sendmail) and does not receive mail, expand aliases or manage a queue. One of its primary uses is for forwarding automated email (like system alerts) off your machine and to an external email address.

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

EmailSuccess is an advanced SMTP Server (MTA) derived from the technology and the expertise accumulated in years of exchanges with the ISP and ESP worlds, built from the ground up to handle the most critical reliability, performance, security, and deliverability requirements.