This allows output to be read with `docker compose logs`.

Signed-off-by: Malfurious <m@lfurio.us>

The encrypted "submissions" port (465) is opened in postfix and is
configured for delivery of outgoing mail of authenticated users only.
The authentication is provided by dovecot via unix socket and account
data is sourced from the userconfig directory.

Signed-off-by: Malfurious <m@lfurio.us>

Setup postfix and dovecot to work with virtual domains/mailboxes and
user accounts defined in the userconfig directory.  Services are also
configured to use TLS certificates that will later be provided by the
nginx-proxy acme service.

Basic formatting and informative comments are added to config files.

Signed-off-by: Malfurious <m@lfurio.us>

Signed-off-by: Malfurious <m@lfurio.us>