Install ISPConfig 3 - Roundcube plugins on Debian 10

Prerequisites

Roundcube has to be installed using apt. If not, you may need to change the file paths used in this tutorial.
Make sure your ISPConfig and Roundcube installation are up to date

Adding a remote user

The ISPConfig 3 plugins use the API to connect to your system. Therefore we need to create a remote user in the control panel.

Log in to your panel, go to System -> Remote Users, and click "Add new remote user". In the form, give your new user a name and a password. I'll use rc-example with the password examplepass. Don't use the same credentials, but create your own. My example panel will be located at https://panel.example.com:8080 with a valid SSL certificate

Enable the following function for your remote user:

Roundcube plugins functions

And enable remote access for the IPv4 and IPv6 address of your webmail server.

Download the plugins

Run the following commands:

cd /tmp
wget https://github.com/w2c/ispconfig3_roundcube/archive/master.zip
unzip master.zip
cd ./ispconfig3_roundcube-master
cp -r ./ispconfig3_* /usr/share/roundcube/plugins
ln -s /usr/share/roundcube/plugins/ispconfig* /var/lib/roundcube/plugins/

The plugins are now in the correct folder, with a symlink from /var/lib/roundcube/plugins. The next step is to configure them to use our remote user. Run this to copy the example config and edit it:

cp /usr/share/roundcube/plugins/ispconfig3_account/config/config.inc.php.dist /usr/share/roundcube/plugins/ispconfig3_account/config/config.inc.php
nano /usr/share/roundcube/plugins/ispconfig3_account/config/config.inc.php

You will see this config file:

$config['identity_limit'] = false;
$config['remote_soap_user'] = '{REMOTE USERNAME}';
$config['remote_soap_pass'] = '{REMOTE PASSWORD}';
$config['soap_url'] = 'https://{YOUR SERVER}:8080/remote/';
$config['soap_validate_cert'] = true;

I'll change this to:

$config['identity_limit'] = false;
$config['remote_soap_user'] = 'rc-example';
$config['remote_soap_pass'] = 'examplepass';
$config['soap_url'] = 'https://panel.example.com:8080/remote/';
$config['soap_validate_cert'] = true;

Make sure to replace the red underlined text with your own credentials and panel address. Change soap_validate_cert to false if you use https but don't have a trusted SSL certificate installed.

Enabling the plugins

To enable the plugins, open the roundcube configuration:

nano /etc/roundcube/config.inc.php

And search for these lines:

// List of active plugins (in plugins/ directory)
$config['plugins'] = array();

To enable the plugins, add this between the brackets:

"jqueryui", "ispconfig3_account", "ispconfig3_autoreply", "ispconfig3_pass", "ispconfig3_spam", "ispconfig3_fetchmail", "ispconfig3_filter", "ispconfig3_forward", "ispconfig3_wblist"

The line will then look like this:

// List of active plugins (in plugins/ directory)
$config['plugins'] = array("jqueryui", "ispconfig3_account", "ispconfig3_autoreply", "ispconfig3_pass", "ispconfig3_spam", "ispconfig3_fetchmail", "ispconfig3_filter", "ispconfig3_forward", "ispconfig3_wblist");

A few notes to this:

The jqueryui plugin has to be placed in front of the other plugins.
If you don't want to use a plugin, for example the fetchmail plugin, leave out ispconfig3_fetchmail.
If you use more than one mailserver, add ispconfig3_autoselect to the list, and leave $config['default_host'] empty. ispconfig3_autoselect will automatically pick the right server for the user that logs in. You can edit it's own configuration file to enable tls/ssl connections between Roundcube and the external mailserver in ispconfig3_autoselect/config/config.inc.php.dist

After saving the configuration file, a new tab "Account" will show up in the webmail settings: