Find Config Files

find /var/www -path "*/config/config.inc.php" 2>/dev/null
find /var/www -path "*/plugins/managesieve/config.inc.php" 2>/dev/null

Example output:

/var/www/<uuid>/public_html/config/config.inc.php
/var/www/<uuid>/public_html/config/config.inc.php

/var/www/<uuid>/public_html/plugins/managesieve/config.inc.php
/var/www/<uuid>/public_html/plugins/managesieve/config.inc.php

Step 1: Find the Container IP

su - roundcubelocal -s /bin/bash -c 'ip addr show eth0 | grep inet'

The host IP is the container IP minus 1.
Example: Container 10.169.0.11 → Host 10.169.0.10

Step 2: Allow Traffic in UFW

ufw allow from <container_ip>

Step 3: Enable the Plugin

Edit config/config.inc.php:

$config['plugins'] = ['password', 'managesieve'];

Step 4: Configure Managesieve

Create plugins/managesieve/config.inc.php:

<?php
$config['managesieve_host'] = 'tls://<host_ip>';
$config['managesieve_conn_options'] = array(
    'ssl' => array(
        'verify_peer' => false,
        'verify_peer_name' => false,
    ),
);