Exim
Exim is a widely used email server software that facilitates the sending and receiving of emails. It is known for its flexibility and configurability, allowing system administrators to tailor it to their specific needs. Exim can handle various email protocols and is often used in Unix-like operating systems.
Originally developed in the 1990s, Exim has become a popular choice for managing email on servers due to its robust features and security options. It supports advanced routing, filtering, and authentication methods, making it suitable for both small and large organizations.