Who needs to read mail when you can even make it receive mail! Make an `smtp.socket`, which calls `smtp.service`, which receives the mail and prints it on stan

Who needs to read mail when you can even make it receive mail! Make an `smtp.socket`, which calls `smtp.service`, which receives the mail and prints it on standard output, which goes to a custom journald namespace (thanks `LogNamespace=mail` in the unit) so you can read your mail with `journalctl --namespace=mail`.