Please take a look at the EmailRelay again http://emailrelay.sourceforge.net/. With latest version 2.5 it can act as a full MTA and deliver mail directly. This makes it a great alternative to Postfix. But unlike Postfix it supports Windows and is small and easier to configure. This makes it extremely valuable especially as a good option for self-hosting.
I created an Ubuntu PPA https://code.launchpad.net/~stokito/+archive/ubuntu/emailrelay It builds debs for amd64 and also for arm64 and Raspberry Pi (armhf). The build works great without any problems.
