Exim
Exim is a free and open-source mail transfer agent (MTA) used for routing, delivering, and receiving email messages on Unix-like operating systems. It is highly configurable and widely deployed in internet-facing mail servers, supporting features like SMTP, message queuing, and spam filtering. Developed at the University of Cambridge, it is known for its flexibility and extensive documentation.
Developers should learn Exim when building or maintaining email infrastructure, such as setting up mail servers for web applications, handling transactional emails, or managing corporate email systems. It is particularly useful in environments requiring custom routing rules, integration with databases for user authentication, or advanced spam and virus scanning, making it a staple in system administration and DevOps roles.