Exim is an open source, cross-platform and freely downloadable command-line software project that has been designed from the offset to act as a MTA (Message Transfer Agent) for GNU/Linux and UNIX-like operating systems. It is targeted mainly at Internet connected UNIX/Linux systems.
Developed at the University of Cambridge
Originally developed at the University of Cambridge, Exim can easily replace the Sendmail MTA software, and it is similar to Smail 3 MTA application, but it includes different configuration than these two.
Can be used for routing mail
Exim is very flexible when it is used for routing mail, and it provides extensive functionality for checking incoming mail. Detailed documentation about how to use Exim is available on the official homepage.
Getting started with Exim
Installing Exim on a GNU/Linux operating systems is quite easy, because it’s a very popular software project and can be found in the main software repositories of major distributions. So, it is recommended to install it from there, via a Software Center app.
In case you want to optimize Exim for your hardware architecture/operating system, or if the latest version is not available in your distro’s software repos, you can install Exim using the source package distributed for free on Softpedia.
You cannot interact with Exim from the command-line, as the software is usually called by Mail User Agents. However, you should check its official documentation for various arguments and options that allow you to control what it does when called. Also check out its man page.
Under the hood
Taking a look under the hood of the Exim project, we can notice that it has been written in the C programming language, which means that is very fast and low on resources. It is compatible with both 64 and 32-bit instruction set architectures.