Steps to reproduce:

$ docker run -t --entrypoint /bin/bash kolab/guam -s
[root@0ba5806f085f guam.git]# erl -pa apps/*/ebin deps/*/ebin -config app -s kolab_guam

Docker image is built from https://github.com/kanarip/kolab-atomicapp/blob/master/03-guam/Dockerfile

The original entrypoint takes in environment variables KOLAB_IMAPF_EXT_SERVICE_HOST (the IP address of the target IMAP server), and sets { tls, true } in /root/guam.git/app.config. The aforementioned example command-line does neither of the substitions.

Guam ends up listening on 0.0.0.0:1936 only.