I've managed to install and start Apache James.
When I try to connect on the WebAdmin it says:
{"statusCode":404,"type":"notFound","message":"GET / can not be found","details":null}
So I am not able to access the WebAdmin. I followed the official documentation... installing jdk 11, downloading JPA Guice binary, configuring and then run.
From documentation I understand that the only file conf for WebAdmin is conf/webadmin.properties but in this file there's only the parameters for port and host.