OpenSMTPD Alternatives

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

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.

Inbucket is an email testing application; it will accept messages for any email address and make them available to view via a web interface.

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.

Haraka is an open source SMTP server written in Node.js which provides extremely high performance coupled with a flexible plugin system allowing Javascript programmers full access to change the behaviour of the server.

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.

A lightweight mail server with SMTP and POP3 support. It mainly used as store-and-forward mail server with POP access to spooled messages or it can be used as a personal internet mail server.

Lettre is a mailer library for Rust.