Please confirm that courier-imapd service is running on the system.

Ajenti is installed under default $PYTHONPATH, typically /usr/lib/python2.?/(dist|site)-packages
Plugins are installed into /var/lib/ajenti/plugins
Scripts are /usr/bin/ajenti-panel and /usr/bin/ajenti-ssl-gen

It's impossible to select a website using just an IP (even in theory). The website with the "Default" flag on the port 80 will be used, or a random one if none of them has a Default port.

If you need to test your websites separately, add an extra different port for each and use those.

Are you asking regarding Ajenti V? Yes, you can test your stuff using the IP. It doesn't depend on panel or webserver.

В /etc/ajenti/config.json порт можно сменить ("port")

Добавил внизу http://support.ajenti.org/topic/507352-troubleshooting/

См. пожалуйста http://support.ajenti.org/topic/507352-troubleshooting/

Use Reverse proxy content type and http://localhost:8080 as its URL.

Please upload complete file to Gist or something. Also make sure that all Configuration checks under Websites are ok.