diff -urN ../roundcubemail-1.5.0.orig/plugins/managesieve/config.inc.php.dist ./plugins/managesieve/config.inc.php.dist
--- ../roundcubemail-1.5.0.orig/plugins/managesieve/config.inc.php.dist	2021-10-17 23:38:04.000000000 +0300
+++ ./plugins/managesieve/config.inc.php.dist	2021-11-27 17:46:27.955930000 +0200
@@ -44,6 +44,9 @@
 // A file with default script content (e.g. spam filter)
 $config['managesieve_default'] = '/etc/dovecot/sieve/global';
 
+// prefix contents of root user filters script
+$config['managesieve_user_root_prefix'] = "require [\"include\"];\r\ninclude :global \"global-spam\";\r\n";
+
 // The name of the script which will be used when there's no user script
 $config['managesieve_script_name'] = 'managesieve';
 
diff -urN ../roundcubemail-1.5.0.orig/plugins/managesieve/lib/Roundcube/rcube_sieve.php ./plugins/managesieve/lib/Roundcube/rcube_sieve.php
--- ../roundcubemail-1.5.0.orig/plugins/managesieve/lib/Roundcube/rcube_sieve.php	2021-10-17 23:38:04.000000000 +0300
+++ ./plugins/managesieve/lib/Roundcube/rcube_sieve.php	2021-11-27 17:47:39.860653000 +0200
@@ -34,6 +34,8 @@
     public $script;                 // rcube_sieve_script object
     public $current;                // name of currently loaded script
 
+    public $managesieve_user_root_prefix;
+
     const ERROR_CONNECTION = 1;
     const ERROR_LOGIN      = 2;
     const ERROR_NOT_EXISTS = 3;    // script not exists
@@ -407,6 +409,20 @@
 
         // fix/convert to Roundcube format
         if (!empty($script->content)) {
+
+            if ((!empty($this->managesieve_user_root_prefix)) and (is_array($script->content))) {
+                $script_user_root_prefix = new rcube_sieve_script($this->managesieve_user_root_prefix, $this->exts);
+                if ((!empty($script_user_root_prefix->content)) and (is_array($script_user_root_prefix->content))) {
+                    while ($prefix_rule = array_pop($script_user_root_prefix->content)) {
+                        $found = false;
+                        foreach ($script->content as $rule) {
+                            if ($rule == $prefix_rule) $found = true;
+                        }
+                        if (!$found) array_unshift($script->content, $prefix_rule);
+                    }
+                }
+            }
+
             // replace all elsif with if+stop, we support only ifs
             foreach ($script->content as $idx => $rule) {
                 if (empty($rule['type']) || !preg_match('/^(if|elsif|else)$/', $rule['type'])) {
diff -urN ../roundcubemail-1.5.0.orig/plugins/managesieve/lib/Roundcube/rcube_sieve_engine.php ./plugins/managesieve/lib/Roundcube/rcube_sieve_engine.php
--- ../roundcubemail-1.5.0.orig/plugins/managesieve/lib/Roundcube/rcube_sieve_engine.php	2021-10-17 23:38:04.000000000 +0300
+++ ./plugins/managesieve/lib/Roundcube/rcube_sieve_engine.php	2021-11-27 17:48:44.145145000 +0200
@@ -229,6 +229,7 @@
                 ], true, false
             );
         }
+        $this->sieve->managesieve_user_root_prefix = $this->rc->config->get('managesieve_user_root_prefix');
 
         return $error;
     }
@@ -2986,6 +2987,7 @@
                     ."#\n"
                     ."# For more information, see http://wiki.kolab.org/KEP:14#USER\n"
                     ."#\n";
+                $content .= $this->rc->config->get('managesieve_user_root_prefix');
 
                 if ($this->sieve->save_script('USER', $content)) {
                     $_SESSION['managesieve_user_script'] = 'USER';