keycat/keycatd repository overview

⁠tl;dr

You can run KeyCat as

docker run -v /etc/ssl:/etc/ssl -v /opt/keycat/keycatd.toml:/etc/keycat/keycatd.toml -p 23764:23764 keycat/keycatd

⁠KeyCat docker container

This docker image only contains the keycatd binary so all other required bits need to be mounted. That's why /etc/ssl has to be mounted. If it is not mounted keycatd cannot check certificate validities when contacting external services like mail servers to send mail. The rest is pretty obvious. Just set up a postgresql db, mail server and follow the instructions in KeyCat server repo⁠