Axigen is a free mail server.
At the time of writing, the free version of Axigen allows you to configure up to 5 domains, 5 users and 5 groups.
Depending on the operating system, copy the link to the latest version https://www.axigen.com/mail-server/download/
For example, I copied the link to the DEB package, as I will install on Ubuntu Server 18.04.
We read the license agreement, agree with it and select “Install axigen”.
Upon completion of the installation, open http://hostname:9000 in the browser and follow the instructions.
After installation, the following ports will be used for:
127.0.0.1, port 7000 CLI (Command Line Interface)
All interfaces, ports 25 and 465 SSLSMTP Incoming
All interfaces, ports 143 and 993 SSLIMAP
All interfaces, ports 80 and 443 SSLWebMail
All interfaces, ports 9000 and 9443 SSLWebAdmin
All interfaces, port 21 FTP Backup
See also my article:
Installing and configuring iRedMail