DBMail Docker support is experimental and is focused on dbmail-3.3.
You need a copy of the 3.3.x branch of the source code available from https://github.com/dbmail/dbmail/ with the Dockerfile in the docker directory https://github.com/dbmail/dbmail/tree/master/docker
Configuration is currently only available in dbmail.conf, so copy dbmail.conf to docker/dbmail.conf and edit with your configuration. TLS is not included in this version but is easy to add, simply add your certificates in the DBMail container (copy your ca, cert and key into docker/tls/, amend the tls_cafile, tls_cert and tls_key entries in dbmail.conf, then add the following to the Dockerfile.
COPY docker/tls/* /usr/local/etc/"
You may wish to review logging
file_logging_levels = 31
syslog_logging_levels = 0
logfile = /var/log/dbmail-imapd.log
errorlog = /var/log/dbmail-imapd.err
To create the dbmail image use the docker cli as follows:
docker image build --file docker/Dockerfile --tag dbmail:latest .
The image is based on Deban Jammy and is currently about 180Mb.
Create and run the container with the docker cli:
docker run -p 143:143 -p 993:993 dbmail:latest