I've brought up a new docker-mailserver container and am reconfiguring the Roundcube container I'd recently set up that was pointed at my old mail server. It's working as far as basic functionality goes, but it's still not communicating with Sieve. On the docker-mailserver side, ENABLE_MANAGESIEVE=1 is set and the container is set to expose port 4190. ```docker exec -it roundcube nc <hostname> 4190``` returns a response that suggests that managesieve is up and running and that the Roundcube container can connect to it. On the Roundcube side, plugins/managesieve/config.inc.php was copied over from config.inc.php.dist and managesieve_host was set to <hostname>:4190. I then restarted both the mail server and Roundcube. When I click on filter settings in Roundcube, though, I still get the "unable to connect to server" error.
I also tried setting managesieve_auth_type from null to PLAIN, but that keeps Roundcube from working at all. From the description, it seems that null should work.
I've downloaded the Sieve Windows app and connected it to the server, knocked together a script (first time, as I've used procmail on my old server), and tested it. It worked as expected, so it would appear that everything within docker-mailserver is working properly and it's just Roundcube and its managesieve plugin that don't want to play ball for some reason.
Update: I figured it out...needed the following in plugins/managesieve/config.inc.php:
$config['managesieve_host'] = 'tls://<hostname>';
$config['managesieve_auth_type'] = "PLAIN";
PLAIN didn't work earlier because it wasn't quoted.