Best Communication - Email - Mail Transfer Agents software in 2026

chasquid

blitiri.com.ar

Open source

SMTP (email) server with a focus on simplicity, security, and ease of operation.

Courier MTA

courier-mta.org

Open source

Fast, scalable, enterprise mail/groupware server providing ESMTP, IMAP, POP3, webmail, mailing list, basic web-based calendaring and scheduling services.

DragonFly

github.com

Open source

A small MTA for home and office use. Works on Linux and FreeBSD.

EmailRelay

emailrelay.sourceforge.net

Open source

A small and easy to configure SMTP and POP3 server for Windows and Linux.

Exim

exim.org

Open source

Message transfer agent (MTA) developed at the University of Cambridge.

Haraka

haraka.github.io

Open source

Fast, highly extensible, and event driven SMTP server.

OpenSMTPD

opensmtpd.org

Open source

Secure SMTP server implementation from the OpenBSD project.

OpenTrashmail

github.com

Open source

Complete trashmail solution that exposes an SMTP server and has a web interface to manage received emails. Works with multiple and wildcard domains and is fully file based (no database needed). Includes RSS feeds and JSON API.

Postfix

postfix.org

Open source

Fast, easy to administer, and secure Sendmail replacement.

Sendmail

proofpoint.com

Open source

Message transfer agent (MTA).