diff --git a/plugins/managesieve/lib/Roundcube/rcube_sieve_engine.php b/plugins/managesieve/lib/Roundcube/rcube_sieve_engine.php
index 3bb5eacc5..b6a39f08f 100644
--- a/plugins/managesieve/lib/Roundcube/rcube_sieve_engine.php
+++ b/plugins/managesieve/lib/Roundcube/rcube_sieve_engine.php
@@ -595,6 +595,7 @@ class rcube_sieve_engine
             // and arrays
             $headers        = rcube_utils::get_input_value('_header', rcube_utils::INPUT_POST);
             $cust_headers   = rcube_utils::get_input_value('_custom_header', rcube_utils::INPUT_POST);
+            $cust_vars      = rcube_utils::get_input_value('_custom_var', rcube_utils::INPUT_POST);
             $ops            = rcube_utils::get_input_value('_rule_op', rcube_utils::INPUT_POST);
             $sizeops        = rcube_utils::get_input_value('_rule_size_op', rcube_utils::INPUT_POST);
             $sizeitems      = rcube_utils::get_input_value('_rule_size_item', rcube_utils::INPUT_POST);
@@ -854,6 +855,7 @@ class rcube_sieve_engine
                     }
                     else {
                         $cust_header = $headers = $this->strip_value(array_shift($cust_headers));
+                        $cust_var    = $headers = $this->strip_value(array_shift($cust_vars));
                         $mod         = $this->strip_value($mods[$idx]);
                         $mod_type    = $this->strip_value($mod_types[$idx]);
                         $index       = $this->strip_value($indexes[$idx]);
@@ -868,10 +870,10 @@ class rcube_sieve_engine
                             $this->form['tests'][$i]['last']  = !empty($indexlast);
                         }
 
-                        if ($header == '...') {
+                        if ($header == '...' || $header == 'string') {
                             if (!count($headers))
                                 $this->errors['tests'][$i]['header'] = $this->plugin->gettext('cannotbeempty');
-                            else {
+                            else if ($header == '...') {
                                 foreach ($headers as $hr) {
                                     // RFC2822: printable ASCII except colon
                                     if (!preg_match('/^[\x21-\x39\x41-\x7E]+$/i', $hr)) {
@@ -881,9 +883,11 @@ class rcube_sieve_engine
                             }
 
                             if (empty($this->errors['tests'][$i]['header']))
-                                $cust_header = (is_array($headers) && count($headers) == 1) ? $headers[0] : $headers;
+                                $cust_header = $cust_var = (is_array($headers) && count($headers) == 1) ? $headers[0] : $headers;
                         }
 
+                        $test   = $header == 'string' ? 'string' : 'header';
+                        $header = $header == 'string' ? $cust_var : $header;
                         $header = $header == '...' ? $cust_header : $header;
 
                         if (is_array($header)) {
@@ -899,8 +903,6 @@ class rcube_sieve_engine
                             $this->form['tests'][$i]['arg'] = $header;
                         }
                         else {
-                            $test = 'header';
-
                             if ($mod == 'address' || $mod == 'envelope') {
                                 $found = false;
                                 if (empty($this->errors['tests'][$i]['header'])) {
@@ -1446,6 +1448,9 @@ class rcube_sieve_engine
         if (in_array('body', $this->exts)) {
             $select_header->add($this->plugin->gettext('body'), 'body');
         }
+        if (in_array('variables', $this->exts)) {
+            $select_header->add($this->plugin->gettext('string'), 'string');
+        }
         $select_header->add($this->plugin->gettext('size'), 'size');
         if (in_array('date', $this->exts)) {
             $select_header->add($this->plugin->gettext('datetest'), 'date');
@@ -1472,7 +1477,7 @@ class rcube_sieve_engine
                 $matches = ($header = strtolower($rule['arg'])) && isset($this->headers[$header]);
                 $test    = $matches ? $header : '...';
             }
-            else if (in_array($rule['test'], array('size', 'body', 'date', 'currentdate'))) {
+            else if (in_array($rule['test'], array('size', 'body', 'date', 'currentdate', 'string'))) {
                 $test = $rule['test'];
             }
             else if (in_array($rule['test'], array('duplicate'))) {
@@ -1492,6 +1497,12 @@ class rcube_sieve_engine
                 unset($custom);
             }
         }
+        else if (isset($rule['test']) && $rule['test'] == 'string') {
+            $customv = (array) $rule['arg1'];
+            if (count($customv) == 1 && isset($this->headers[strtolower($customv[0])])) {
+                unset($customv);
+            }
+        }
         else if (isset($rule['test']) && $rule['test'] == 'exists') {
             $custom = (array) $rule['arg'];
             if (count($custom) == 1 && isset($this->headers[strtolower($custom[0])])) {
@@ -1499,9 +1510,13 @@ class rcube_sieve_engine
             }
         }
 
+        // custom variable input
         $tout = $this->list_input($id, 'custom_header', $custom, isset($custom),
             $this->error_class($id, 'test', 'header', 'custom_header'), 15) . "\n";
 
+        $tout .= $this->list_input($id, 'custom_var', $customv, isset($customv),
+            $this->error_class($id, 'test', 'header', 'custom_var'), 15) . "\n";
+
         // matching type select (operator)
         $select_op = new html_select(array('name' => "_rule_op[]", 'id' => 'rule_op'.$id,
             'style' => 'display:' .(!in_array($rule['test'], array('size', 'duplicate')) ? 'inline' : 'none'),
@@ -1538,7 +1553,7 @@ class rcube_sieve_engine
         $target = '';
 
         // target(s) input
-        if (in_array($rule['test'], array('header', 'address', 'envelope'))) {
+        if (in_array($rule['test'], array('header', 'address', 'envelope','string'))) {
             $target = $rule['arg2'];
         }
         else if (in_array($rule['test'], array('body', 'date', 'currentdate'))) {
@@ -1625,7 +1640,7 @@ class rcube_sieve_engine
             $select_type->add(rcube::Q($this->plugin->gettext('detail')), 'detail');
         }
 
-        $need_mod = !in_array($rule['test'], array('size', 'body', 'date', 'currentdate', 'duplicate'));
+        $need_mod = !in_array($rule['test'], array('size', 'body', 'date', 'currentdate', 'duplicate', 'string'));
         $mout = '<div id="rule_mod' .$id. '" class="adv"' . (!$need_mod ? ' style="display:none"' : '') . '>';
         $mout .= ' <span class="label">' . rcube::Q($this->plugin->gettext('modifier')) . ' </span>';
         $mout .= $select_mod->show($rule['test']);
@@ -1765,7 +1780,7 @@ class rcube_sieve_engine
             $rule['type'] = $rule['type'] == 'over' ? 'under' : 'over';
         }
 
-        $set = array('header', 'address', 'envelope', 'body', 'date', 'currentdate');
+        $set = array('header', 'address', 'envelope', 'body', 'date', 'currentdate', 'string');
 
         // build test string supported by select element
         if ($rule['size']) {
diff --git a/plugins/managesieve/lib/Roundcube/rcube_sieve_script.php b/plugins/managesieve/lib/Roundcube/rcube_sieve_script.php
index b6a121b7b..66d687e2e 100644
--- a/plugins/managesieve/lib/Roundcube/rcube_sieve_script.php
+++ b/plugins/managesieve/lib/Roundcube/rcube_sieve_script.php
@@ -238,8 +238,13 @@ class rcube_sieve_script
                         break;
 
                     case 'header':
+                    case 'string':
+                        if ($test['test'] == 'string') {
+                            array_push($exts, 'variables');
+                        }
+                        
                         $tests[$i] .= ($test['not'] ? 'not ' : '');
-                        $tests[$i] .= 'header';
+                        $tests[$i] .= $test['test'];
 
                         $this->add_index($test, $tests[$i], $exts);
                         $this->add_operator($test, $tests[$i], $exts);
@@ -707,6 +712,7 @@ class rcube_sieve_script
                 break;
 
             case 'header':
+            case 'string':
             case 'address':
             case 'envelope':
                 $test = array('test' => $token, 'not' => $not);
@@ -716,7 +722,7 @@ class rcube_sieve_script
 
                 $test += $this->test_tokens($tokens);
 
-                if ($token != 'header' && !empty($tokens)) {
+                if ($token != 'header' && $token != 'string' && !empty($tokens)) {
                     for ($i=0, $len=count($tokens); $i<$len; $i++) {
                         if (!is_array($tokens[$i]) && preg_match('/^:(localpart|domain|all|user|detail)$/i', $tokens[$i])) {
                             $test['part'] = strtolower(substr($tokens[$i], 1));
diff --git a/plugins/managesieve/localization/en_CA.inc b/plugins/managesieve/localization/en_CA.inc
index 1850bbb01..6b66d13a8 100644
--- a/plugins/managesieve/localization/en_CA.inc
+++ b/plugins/managesieve/localization/en_CA.inc
@@ -122,6 +122,7 @@ $labels['filtercreate'] = 'Create filter';
 $labels['usedata'] = 'Use following data in the filter:';
 $labels['nextstep'] = 'Next Step';
 $labels['...'] = '...';
+$labels['string'] = 'String';
 $labels['currdate'] = 'Current date';
 $labels['datetest'] = 'Date';
 $labels['dateheader'] = 'header:';
diff --git a/plugins/managesieve/localization/en_GB.inc b/plugins/managesieve/localization/en_GB.inc
index e9433491c..b51385310 100644
--- a/plugins/managesieve/localization/en_GB.inc
+++ b/plugins/managesieve/localization/en_GB.inc
@@ -122,6 +122,7 @@ $labels['filtercreate'] = 'Create filter';
 $labels['usedata'] = 'Use following data in the filter:';
 $labels['nextstep'] = 'Next Step';
 $labels['...'] = '...';
+$labels['string'] = 'String';
 $labels['currdate'] = 'Current date';
 $labels['datetest'] = 'Date';
 $labels['dateheader'] = 'header:';
diff --git a/plugins/managesieve/localization/en_US.inc b/plugins/managesieve/localization/en_US.inc
index c15193d66..8cd8c231d 100644
--- a/plugins/managesieve/localization/en_US.inc
+++ b/plugins/managesieve/localization/en_US.inc
@@ -126,6 +126,7 @@ $labels['filtercreate'] = 'Create filter';
 $labels['usedata'] = 'Use following data in the filter:';
 $labels['nextstep'] = 'Next Step';
 $labels['...'] = '...';
+$labels['string'] = 'String';
 $labels['currdate'] = 'Current date';
 $labels['datetest'] = 'Date';
 $labels['dateheader'] = 'header:';
diff --git a/plugins/managesieve/localization/fr_FR.inc b/plugins/managesieve/localization/fr_FR.inc
index ef02e7fd2..95a435020 100644
--- a/plugins/managesieve/localization/fr_FR.inc
+++ b/plugins/managesieve/localization/fr_FR.inc
@@ -124,6 +124,7 @@ $labels['filtercreate'] = 'Créer un filtre';
 $labels['usedata'] = 'Utiliser les données suivantes dans le filtre :';
 $labels['nextstep'] = 'Étape suivante';
 $labels['...'] = '...';
+$labels['string'] = 'Chaîne';
 $labels['currdate'] = 'Date actuelle';
 $labels['datetest'] = 'Date';
 $labels['dateheader'] = 'en-tête :';
diff --git a/plugins/managesieve/managesieve.js b/plugins/managesieve/managesieve.js
index 1316a5aa5..cfc60db7f 100644
--- a/plugins/managesieve/managesieve.js
+++ b/plugins/managesieve/managesieve.js
@@ -602,6 +602,7 @@ function rule_header_select(id)
     msg = document.getElementById('rule_message' + id),
     op = document.getElementById('rule_op' + id),
     header = document.getElementById('custom_header' + id + '_list'),
+    custstr = document.getElementById('custom_var' + id + '_list'),
     mod = document.getElementById('rule_mod' + id),
     trans = document.getElementById('rule_trans' + id),
     comp = document.getElementById('rule_comp' + id),
@@ -611,18 +612,19 @@ function rule_header_select(id)
 
   if (h == 'size') {
     size.style.display = 'inline';
-    $.each([op, header, mod, trans, comp, msg], function() { this.style.display = 'none'; });
+    $.each([op, header, custstr, mod, trans, comp, msg], function() { this.style.display = 'none'; });
   }
   else if (h == 'message') {
     msg.style.display = 'inline';
-    $.each([op, header, mod, trans, comp, size], function() { this.style.display = 'none'; });
+    $.each([op, header, custstr, mod, trans, comp, size], function() { this.style.display = 'none'; });
   }
   else {
     header.style.display = h != '...' ? 'none' : 'inline-block';
+    custstr.style.display = h != 'string' ? 'none' : 'inline-block';
     size.style.display = 'none';
     op.style.display = 'inline';
     comp.style.display = '';
-    mod.style.display = h == 'body' || h == 'currentdate' || h == 'date' ? 'none' : 'block';
+    mod.style.display = h == 'body' || h == 'currentdate' || h == 'date' || h == 'string' ? 'none' : 'block';
     trans.style.display = h == 'body' ? 'block' : 'none';
     msg.style.display = h == 'message' ? 'block' : 'none';
   }
@@ -634,7 +636,9 @@ function rule_header_select(id)
 
   rule_op_select(op, id, h);
   rule_mod_select(id, h);
-  obj.style.width = h == '...' ? '40px' : '';
+  
+  if (h == '...') obj.style.width = '40px';
+  else if (h == 'string') obj.style.width = '90px';
 };
 
 function rule_op_select(obj, id, header)
@@ -668,7 +672,7 @@ function rule_mod_select(id, header)
   target.style.display = obj.value != 'address' && obj.value != 'envelope' ? 'none' : 'inline';
 
   if (index)
-    index.style.display = !header.match(/^(body|currentdate|size|message)$/) && obj.value != 'envelope'  ? '' : 'none';
+    index.style.display = !header.match(/^(body|currentdate|size|message|string)$/) && obj.value != 'envelope'  ? '' : 'none';
 
   if (duplicate)
     duplicate.style.display = header == 'message' ? '' : 'none';
@@ -903,6 +907,7 @@ function sieve_form_init()
   // small resize for header element
   $('select[name="_header[]"]', rcmail.gui_objects.sieveform).each(function() {
     if (this.value == '...') this.style.width = '40px';
+    if (this.value == 'string') this.style.width = '90px';
   });
 
   // resize dialog window