Exim Internet Mailer

Exim is a free, open-source message transfer agent (MTA) for Unix-like systems that handles routing, delivery, and security checking of email, targeted at system administrators running mail servers.

🚀 Overview

Exim is a highly configurable mail transfer agent (MTA) originally developed at the University of Cambridge for Unix systems connected to the Internet. It can replace Sendmail or other MTAs while offering greater flexibility in mail routing, delivery, and incoming mail verification.

What problem does this project solve? Exim solves the need for a reliable, customizable MTA that supports complex routing rules, access controls, and integration with spam/virus scanners on Internet-connected servers.

Who is it built for? It's built for system administrators and developers managing email infrastructure on Unix-like operating systems like Linux, FreeBSD, and Solaris.

Why did you build it? Originally created to provide a more general and powerful alternative to Smail 3 and Sendmail, with entirely new code emphasizing ease of configuration and extensibility.

✨ Key Features

Highly flexible mail routing and configuration via a single text file with a powerful string expansion language and macros
Access Control Lists (ACLs) for detailed checking of incoming SMTP mail, enabling spam prevention and policy enforcement
Support for SMTP/LMTP over TCP/IP (IPv6), pipe/file transports, content scanning extensions for malware/spam
Optional Eximon X11 monitor for real-time graphical administration of queues and logs
Optional: Beta versions available for testing new features

🛠 Tech Stack

Core: C (91.4%), Perl (testsuite 5.5%), Shell scripts
Build: Makefile
Documentation: HTML specification and PDF
No web frontend/backend; daemon-based server software
Hosting: Self-hosted on Unix-like systems; distributions via FTP

👥 Who Is This For?

This project is useful for:

Developers who want to customize email routing and delivery logic
Teams looking for a Sendmail-compatible MTA with advanced ACLs and scanning
Indie makers building mail servers on Linux/Unix without bulk spam capabilities

📸 Screenshots / Demo

Live demo: N/A (command-line/server software)
GitHub: https://github.com/Exim/exim
Official Git: https://code.exim.org/exim/exim.git

🔥 Project Status

🟡 Maintained

Last updated: 2026-03-24

❓ FAQ

Is this project free?

Yes / Open Source (Freely available under the GNU General Public License (GPL).)

Is the source code available?

Yes — https://github.com/Exim/exim or official https://code.exim.org/exim/exim.git, downloads at https://ftp.exim.org/pub/exim/

Can I contribute?

Report bugs at https://bugs.exim.org/, discuss development on exim-dev@exim.org mailing list, submit patches via git or mailing list. Edit the wiki at https://wiki.exim.org/ after login from code.exim.org. Join IRC #exim on irc.libera.chat.