First I highly recommend using a newer PHP version, PHP 5.6 hasn't been support since 2018 and shouldn't be used anymore.

If you have to use PHP 5.6 that last branch of Roundcube that support PHP 5.6 is the 1.5.x branch its still available as an LTS.

Can someone help me install the correct version to work with PHP 5.6?
I use aaPanel Linux where I work with the system System: Alma 9.5 (Teal Serval) x86_64(Py3.12.3) and I have installed the Mail Server 7.3.3 Plugin where I have configured it and it works great I receive and send emails normally but I would like to put RoundCube in my Domain Name mail.mydomain.xyz

It has come to my attention that anyone who registered for an account on the forum since May 1st 2025 didn't get an email to allow them to verify there account and complete the registration process. I've implemented a fix for the issue and have resent the verification emails to everyone effected by this issue.

If you run into any issues activating your account on the forum please reach out to me through my website https://skaero.com

Is there someone who can help? Thank you again!!

Thank you.    Yes it does run that .sh file.

I had to disable this one as well:  Purge expired Roundcube sessions, caches and tempfiles

Roundcube on my server is rarely used.   Its just a backup in case I need web access somewhere.

SKaero, you're great! Thank you so much for your help!
Here is my final autologon plugin:
<?php

/**
 * Sample plugin to try out some hooks.
 * This performs an automatic login if accessed from localhost
 *
 * @license GNU GPLv3+
 * @author Thomas Bruederli
 */

class autologon extends rcube_plugin
{
    public function init()
    {
        $this->add_hook('startup', [$this, 'startup']);
        $this->add_hook('authenticate', [$this, 'authenticate']);
        $this->add_hook('ready', [$this, 'ready']);
    }

    function startup($args)
    {
        if (empty($_SESSION['user_id']) && !empty($_GET['_autologin'])) {
            $args['action'] = 'login';
        }
        return $args;
    }

    function ready($args)
    {
        if (!empty($_GET['_autologin']) && $_GET['_user'] != $_SESSION['username']){
            $rcmail = rcmail::get_instance();
            $rcmail->logout_actions();
            $rcmail->kill_session();
            header("Location: https://" . gethostname() . "/?_autologin=1&_user={$_GET['_user']}&_token={$_GET['_token']}");
        }
        return $args;
    }

    function authenticate($args)
    {
        if (!empty($_GET['_autologin'])){
            $args['user']        = $_GET['_user'];
            $cmd = '/usr/bin/python3 /usr/share/mpd/maila/manage.py user decode -u '.$_GET['_user'].' -t '.$_GET['_token'];
            $output = shell_exec(escapeshellcmd($cmd));
            if (!empty($output)){
                $out = trim($output);
            }
            else {
                return $args;
            }
            $args['pass']        = $out;
            $args['host']        = 'localhost';
            $args['cookiecheck'] = false;
            $args['valid']       = true;
        }
        return $args;
    }
}
It works like a charm.

I would use a header redirect that way the login can be handled by the other part of the plugin that is already working.

I don't understand, how to redirect back to the login.
Now my ready function is like this:
    function ready($args)
    {
        if (!empty($_GET['_autologin'])){
            if ($_GET['_user'] != $args['user']){
                $rcmail = rcmail::get_instance();
                $rcmail->logout_actions();
                $rcmail->kill_session();
                $this->authenticate($args);
            }
        }
        return $args;
    }If I send GET request with autologin parameter first time, the users mailbox is opened. Then I send GET request with new user. Login page with new username and empty password is opend. When I send GET request with new user again, the new users mailbox is opend.
I've tried to use $rcmail->login("new_user*master_user", "master_password", "localhost", false); instead of $this->authenticate($args);. New user mailbox is opend for a second and then redirects to empty login page.
How to redirect back to the login from the ready function correctly?

There is an example of how to log a user out in the autologout plugin https://github.com/roundcube/roundcubemail/blob/master/plugins/autologout/autologout.php you can then redirect to the login again to login with the new account.