Discovered them recently. Price looks absolutely fair for what you get. It offers up to ten external addresses for sending and has a web interface so it looks like a solid Gmail alternative.
When the Debian install asks you what device to use, give it /dev/sda or /dev/vda. For some reason /dev/cdrom wasn't working for me either. I ended up switching the ISO's device to virtio and tried /dev/vda and it worked.
The ISO was on /dev/vda and the target disk image was on /dev/vdb. Just make sure you install the bootloader on the disk image. Then when I removed the ISO, everything was just fine.
Magma is an email server, supporting many of the common email protocols, designed with security in mind. It was designed and used by the guys at Lavabit (of Edward Snowden fame).
It combines outgoing (SMTP) and incoming (POP, *MAP) functionality, so it would be like using Dovecot and Postfix (rival mail server products) together.
It requires that you have a relational database (the documents describe MySql) and a key-value store (the documents describe Memcache) to support it and the documentation suggests it's designed for Linux (specifically with instructions for CentOS, which is a Red Hat distro). A mail server is generally installed on an "always-on" computer connected to the internet-connected network.
Note that even though it's "designed with security in mind", I don't see any mention of a security audit on either the linked page or the GitHub repo.