Insular email distribution - mail server as Docker images
Mailu is a simple yet full-featured mail server as a set of Docker images. It is free software (both as in free beer and as in free speech), open to suggestions and external contributions. The project aims at providing people with an easily setup, easily maintained and full-featured mail server while not shipping proprietary software nor unrelated features often found in popular groupware. Security, enforced TLS, DANE, MTA-STS, Letsencrypt!
...Please see https://sourceforge.net/p/formavid/code/ci/master/tree/INSTALL.txt for details. The appliance is specially designed to run on the Google Cloud Platform "Free Tier" https://formavid.org/gce and has it's own custom install script https://sourceforge.net/projects/formavid/files/gcloud-gce-deployment/download with instructions https://sourceforge.net/projects/formavid/files/ provided.
RadicalSpam is a free and open source package distributed under GPL v2, including products such as Postfix, SpamAssassin Amavisd-new, Clamav, Razor, DCC, Postgrey, Bind; providing a secure SMTP relay, ready to use with linux and docker environement. More information : http://www.radical-spam.org