I have an issue with this line when SELinux is on.

https://github.com/tomav/docker-mailserver/blob/108bdbd46361b23671b11940cf5827a98f6975b0/setup.sh#L169

Editing the script and adding :Z fixes the issue.
-v "${CONFIG_PATH}":/tmp/docker-mailserver:Z \

I would do a PR but unsure of the best way to detect SELinux running.