A colleague at work (in the US) found that his ISP was going to outsource his email to Microsoft and charge $25/month for that.  He poked around, and found his own personal "outsourcing" in the form of the following...
https://github.com/tomav/docker-mailserver

Explained further here: https://tvi.al/simple-mail-server-with-docker/
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When confronted by a difficult problem, solve it by reducing it to the
question, "How would the Lone Ranger handle this?"