OpenSMTPD Alternatives

Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail.

sSMTP is a simple MTA to deliver mail from a computer to a mail server.

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Exim is a message transfer agent (MTA) developed at the University of Cambridge for use on Unix systems connected to the Internet.

Open Source

Sendmail is a general purpose internetwork email routing facility that supports many kinds of...

msmtp is an SMTP client.

A fully fledged, free email server solution, an open source project (GPL v2).

Open Source

A small Mail Transport Agent (MTA), designed for home and office use. Part of ...

Zimbra is trusted by over 500 million users to increase productivity with a complete set of collaboration tools while maintaining total control over security and privacy.

Microsoft Exchange Server is a messaging and collaborative software product developed by Microsoft.

Configure SMTP e-mail in IIS when you want to deliver e-mail messages from your site.

Mail-in-a-Box provides webmail and an IMAP/SMTP server for use with mobile devices and desktop mail software and also includes contacts and calendar synchronization.

Open Source

PowerMTA is an industrial-strength software for high-volume email delivery.

esmtp is a user configurable relay-only Mail Transfer Agent (MTA) with a sendmail compatible syntax.