Email Servers
You may not be aware of it as a user but email is a very complex system to administer, in fact it's a very complex system of other archaic, hard-to-configure, sometimes-interoperable complex systems.
We're going to spend three weeks working on it so that by the end of the course you will have a general understanding of what services are involved in sending, filtering, and reading email. You will also have the skills to configure a basic setup using the default services on CentOS 7.
Overview
This is a simple (yeah, really) diagram of how you can send an email to someone else:
The diagram above doesn't even include reading email, but it's as simple as it gets (if you want to run an email server). You will need to learn to administer basics of all the systems in the diagram. We won't go in too much depth, only the minimum you need. But we will not (for example) go over every detail of Postfix, which on its own has a rather complex diagram.