diff --git a/plugins/calendar/calendar.php b/plugins/calendar/calendar.php
index 9b815bc8..2b37b799 100644
--- a/plugins/calendar/calendar.php
+++ b/plugins/calendar/calendar.php
@@ -150,6 +150,7 @@ class calendar extends rcube_plugin
       $this->register_action('itip-status', array($this, 'event_itip_status'));
       $this->register_action('itip-remove', array($this, 'event_itip_remove'));
       $this->register_action('itip-decline-reply', array($this, 'mail_itip_decline_reply'));
+      $this->register_action('itip-delegate', array($this, 'mail_itip_delegate'));
       $this->register_action('resources-list', array($this, 'resources_list'));
       $this->register_action('resources-owner', array($this, 'resources_owner'));
       $this->register_action('resources-calendar', array($this, 'resources_calendar'));
@@ -239,7 +240,7 @@ class calendar extends rcube_plugin
       $this->itip = new calendar_itip($this);
       
       if ($this->rc->config->get('kolab_invitation_calendars'))
-        $this->itip->set_rsvp_actions(array('accepted','tentative','declined','needs-action'));
+        $this->itip->set_rsvp_actions(array('accepted','tentative','declined','delegated','needs-action'));
     }
 
     return $this->itip;
@@ -957,6 +958,16 @@ class calendar extends rcube_plugin
 
         $ev = $this->driver->get_event($event);
         $ev['attendees'] = $event['attendees'];
+
+        // send invitation to delegatee + add it as attendee
+        if ($status == 'delegated' && $event['to']) {
+          $itip = $this->load_itip();
+          if ($itip->delegate_to($ev, $event['to'], (bool)$event['rsvp'])) {
+            $this->rc->output->show_message('calendar.itipsendsuccess', 'confirmation');
+            $noreply = false;
+          }
+        }
+
         $event = $ev;
 
         if ($success = $this->driver->edit_rsvp($event, $status)) {
@@ -974,6 +985,7 @@ class calendar extends rcube_plugin
               $reply_sender = $attendee['email'];
             }
           }
+
           if (!$noreply) {
             $itip = $this->load_itip();
             $itip->set_sender_email($reply_sender);
@@ -2567,9 +2579,36 @@ class calendar extends rcube_plugin
 
     $error_msg = $this->gettext('errorimportingevent');
     $success = false;
+    $delegate = null;
+
+    if ($status == 'delegated') {
+      $delegates = rcube_mime::decode_address_list(rcube_utils::get_input_value('_to', rcube_utils::INPUT_POST, true), 1, false);
+      $delegate  = reset($delegates);
+
+      if (empty($delegate) || empty($delegate['mailto'])) {
+        $this->rc->output->command('display_message', $this->gettext('libcalendaring.delegateinvalidaddress'), 'error');
+        return;
+      }
+    }
 
     // successfully parsed events?
     if ($event = $this->lib->mail_get_itip_object($mbox, $uid, $mime_id, 'event')) {
+      // forward iTip request to delegatee
+      if ($delegate) {
+        $rsvpme = intval(rcube_utils::get_input_value('_rsvp', rcube_utils::INPUT_POST));
+
+        $itip = $this->load_itip();
+        if ($itip->delegate_to($event, $delegate, $rsvpme ? true : false)) {
+          $this->rc->output->show_message('calendar.itipsendsuccess', 'confirmation');
+        }
+        else {
+          $this->rc->output->command('display_message', $this->gettext('itipresponseerror'), 'error');
+        }
+
+        // the delegator is set to non-participant, thus save as non-blocking
+        $event['free_busy'] = 'free';
+      }
+
       // find writeable calendar to store event
       $cal_id = !empty($_REQUEST['_folder']) ? rcube_utils::get_input_value('_folder', rcube_utils::INPUT_POST) : null;
       $dontsave = ($_REQUEST['_folder'] === '' && $event['_method'] == 'REQUEST');
@@ -2692,14 +2731,14 @@ class calendar extends rcube_plugin
             if ($event['_method'] == 'CANCEL')
               $event['status'] = 'CANCELLED';
             // show me as free when declined (#1670)
-            if ($status == 'declined' || $event['status'] == 'CANCELLED')
+            if ($status == 'declined' || $event['status'] == 'CANCELLED' || $event_attendee['role'] == 'NON-PARTICIPANT')
               $event['free_busy'] = 'free';
 
             $success = $this->driver->edit_event($event);
           }
           else if (!empty($status)) {
             $existing['attendees'] = $event['attendees'];
-            if ($status == 'declined')  // show me as free when declined (#1670)
+            if ($status == 'declined' || $event_attendee['role'] == 'NON-PARTICIPANT')  // show me as free when declined (#1670)
               $existing['free_busy'] = 'free';
             $success = $this->driver->edit_event($existing);
           }
@@ -2780,6 +2819,16 @@ class calendar extends rcube_plugin
     }
   }
 
+  /**
+   * Handler for calendar/itip-delegate requests
+   */
+  function mail_itip_delegate()
+  {
+    // forward request to mail_import_itip() with the right status
+    $_POST['_status'] = $_REQUEST['_status'] = 'delegated';
+    $this->mail_import_itip();
+  }
+
   /**
    * Import the full payload from a mail message attachment
    */
diff --git a/plugins/calendar/calendar_ui.js b/plugins/calendar/calendar_ui.js
index 62b263bc..ae745fe5 100644
--- a/plugins/calendar/calendar_ui.js
+++ b/plugins/calendar/calendar_ui.js
@@ -2323,20 +2323,41 @@ function rcube_calendar_ui(settings)
     }
 
     // when the user accepts or declines an event invitation
-    var event_rsvp = function(response)
+    var event_rsvp = function(response, delegate)
     {
       if (me.selected_event && me.selected_event.attendees && response) {
+        // bring up delegation dialog
+        if (response == 'delegated' && !delegate) {
+          rcube_libcalendaring.itip_delegate_dialog(function(data) {
+            data.rsvp = data.rsvp ? 1 : '';
+            event_rsvp('delegated', data);
+          });
+          return;
+        }
+
         // update attendee status
         for (var data, i=0; i < me.selected_event.attendees.length; i++) {
           data = me.selected_event.attendees[i];
           if (settings.identity.emails.indexOf(';'+String(data.email).toLowerCase()) >= 0) {
             data.status = response.toUpperCase();
-            delete data.rsvp;  // unset RSVP flag
+
+            if (data.status == 'DELEGATED') {
+              data['delegated-to'] = delegate.to;
+            }
+            else {
+              delete data.rsvp;  // unset RSVP flag
+
+              if (data['delegated-to']) {
+                delete data['delegated-to'];
+                if (data.role == 'NON-PARTICIPANT' && status != 'DECLINED')
+                  data.role = 'REQ-PARTICIPANT';
+              }
+            }
           }
         }
 
         // submit status change to server
-        var submit_data = $.extend({}, me.selected_event, { source:null, comment:$('#reply-comment-event-rsvp').val() }),
+        var submit_data = $.extend({}, me.selected_event, { source:null, comment:$('#reply-comment-event-rsvp').val() }, (delegate || {})),
           noreply = $('#noreply-event-rsvp:checked').length ? 1 : 0;
 
         // import event from mail (temporary iTip event)
@@ -2347,6 +2368,8 @@ function rcube_calendar_ui(settings)
             _uid:  submit_data._uid,
             _part: submit_data._part,
             _status:  response,
+            _to: (delegate ? delegate.to : null),
+            _rsvp: (delegate && delegate.rsvp) ? 1 : 0,
             _noreply: noreply,
             _comment: submit_data.comment
           });
diff --git a/plugins/calendar/lib/calendar_ui.php b/plugins/calendar/lib/calendar_ui.php
index 722d54fc..e01ecd80 100644
--- a/plugins/calendar/lib/calendar_ui.php
+++ b/plugins/calendar/lib/calendar_ui.php
@@ -886,7 +886,7 @@ class calendar_ui
 
   function event_rsvp_buttons($attrib = array())
   {
-    return $this->cal->itip->itip_rsvp_buttons($attrib, array('accepted','tentative','declined'));
+    return $this->cal->itip->itip_rsvp_buttons($attrib, array('accepted','tentative','declined','delegated'));
   }
 
 }
diff --git a/plugins/calendar/localization/en_US.inc b/plugins/calendar/localization/en_US.inc
index d802153c..b63b9305 100644
--- a/plugins/calendar/localization/en_US.inc
+++ b/plugins/calendar/localization/en_US.inc
@@ -190,6 +190,8 @@ $labels['itipmailbodyaccepted'] = "\$sender has accepted the invitation to the f
 $labels['itipmailbodytentative'] = "\$sender has tentatively accepted the invitation to the following event:\n\n*\$title*\n\nWhen: \$date\n\nInvitees: \$attendees";
 $labels['itipmailbodydeclined'] = "\$sender has declined the invitation to the following event:\n\n*\$title*\n\nWhen: \$date\n\nInvitees: \$attendees";
 $labels['itipmailbodycancel'] = "\$sender has rejected your participation in the following event:\n\n*\$title*\n\nWhen: \$date";
+$labels['itipmailbodydelegated'] = "\$sender has delegated the participation in the following event:\n\n*\$title*\n\nWhen: \$date";
+$labels['itipmailbodydelegatedto'] = "\$sender has delegated the participation in the following event to you:\n\n*\$title*\n\nWhen: \$date";
 
 $labels['itipdeclineevent'] = 'Do you want to decline your invitation to this event?';
 $labels['declinedeleteconfirm'] = 'Do you also want to delete this declined event from your calendar?';
diff --git a/plugins/libcalendaring/lib/libcalendaring_itip.php b/plugins/libcalendaring/lib/libcalendaring_itip.php
index b2ec3b8b..e9be25d9 100644
--- a/plugins/libcalendaring/lib/libcalendaring_itip.php
+++ b/plugins/libcalendaring/lib/libcalendaring_itip.php
@@ -30,7 +30,7 @@ class libcalendaring_itip
     protected $sender;
     protected $domain;
     protected $itip_send = false;
-    protected $rsvp_actions = array('accepted','tentative','declined');
+    protected $rsvp_actions = array('accepted','tentative','declined','delegated');
     protected $rsvp_status  = array('accepted','tentative','declined','delegated');
 
     function __construct($plugin, $domain = 'libcalendaring')
@@ -257,6 +257,61 @@ class libcalendaring_itip
         return $message;
     }
 
+    /**
+     * Forward the given iTip event as delegation to another person
+     *
+     * @param array Event object to delegate
+     * @param mixed Delegatee as string or hash array with keys 'name' and 'mailto'
+     * @return boolean True on success, False on failure
+     */
+    public function delegate_to(&$event, $delegate, $rsvp = false)
+    {
+        if (is_string($delegate)) {
+            $delegates = rcube_mime::decode_address_list($delegate, 1, false);
+            if (count($delegates) > 0) {
+                $delegate = reset($delegates);
+            }
+        }
+
+        $emails = $this->lib->get_user_emails();
+        $me = $this->rc->user->get_identity();
+
+        // find/create the delegate attendee
+        $delegate_attendee = array(
+            'email' => $delegate['mailto'],
+            'name'  => $delegate['name'],
+            'role'  => 'REQ-PARTICIPANT',
+        );
+        $delegate_index = count($event['attendees']);
+
+        foreach ($event['attendees'] as $i => $attendee) {
+          // set myself the DELEGATED-TO parameter
+          if ($attendee['email'] && in_array(strtolower($attendee['email']), $emails)) {
+              $event['attendees'][$i]['delegated-to'] = $delegate['mailto'];
+              $event['attendees'][$i]['status'] = 'DELEGATED';
+              $event['attendees'][$i]['role'] = 'NON-PARTICIPANT';
+              $event['attendees'][$i]['rsvp'] = $rsvp;
+
+              $me['email'] = $attendee['email'];
+              $delegate_attendee['role'] = $attendee['role'];
+          }
+          // the disired delegatee is already listed as an attendee
+          else if (stripos($delegate['mailto'], $attendee['email']) !== false && $attendee['role'] != 'ORGANIZER') {
+              $delegate_attendee = $attendee;
+              $delegate_index = $i;
+              break;
+          }
+        }
+
+        // set/add delegate attendee with RSVP=TRUE and DELEGATED-FROM parameter
+        $delegate_attendee['rsvp'] = true;
+        $delegate_attendee['status'] = 'NEEDS-ACTION';
+        $delegate_attendee['delegated-from'] = $me['email'];
+        $event['attendees'][$delegate_index] = $delegate_attendee;
+
+        $this->set_sender_email($me['email']);
+        return $this->send_itip_message($event, 'REQUEST', $delegate_attendee, 'itipsubjectdelegatedto', 'itipmailbodydelegatedto');
+    }
 
     /**
      * Handler for calendar/itip-status requests
@@ -332,7 +387,7 @@ class libcalendaring_itip
                 $html = html::div('rsvp-status ' . $status_lc, $this->gettext(array(
                     'name' => 'attendee' . $status_lc,
                     'vars' => array(
-                        'delegatedto' => Q($attendee['delegated-to'] ?: '?'),
+                        'delegatedto' => Q($event['delegated-to'] ?: ($attendee['delegated-to'] ?: '?')),
                     )
                 )));
               }
@@ -400,6 +455,8 @@ class libcalendaring_itip
                 if (!empty($attendee['email']) && $attendee['role'] != 'ORGANIZER') {
                     $metadata['attendee'] = $attendee['email'];
                     $rsvp_status = strtoupper($attendee['status']);
+                    if ($attendee['delegated-to'])
+                        $metadata['delegated-to'] = $attendee['delegated-to'];
                     break;
                 }
             }
@@ -498,6 +555,11 @@ class libcalendaring_itip
 
             $buttons[] = html::div(array('id' => 'rsvp-'.$dom_id, 'class' => 'rsvp-buttons', 'style' => 'display:none'), $rsvp_buttons);
             $buttons[] = html::div(array('id' => 'update-'.$dom_id, 'style' => 'display:none'), $update_button);
+
+            // prepare autocompletion for delegation dialog
+            if (in_array('delegated', $this->rsvp_actions)) {
+                $this->rc->autocomplete_init();
+            }
         }
         // for CANCEL messages, we can:
         else if ($method == 'CANCEL') {
@@ -530,8 +592,6 @@ class libcalendaring_itip
             $buttons[] = html::div(array('id' => 'import-'.$dom_id, 'style' => 'display:none'), $import_button);
         }
 
-        // TODO: add option/checkbox to delete this message after update
-
         // pass some metadata about the event and trigger the asynchronous status check
         $metadata['fallback'] = $rsvp_status;
         $metadata['rsvp'] = intval($metadata['rsvp']);
@@ -539,7 +599,9 @@ class libcalendaring_itip
         $this->rc->output->add_script("rcube_libcalendaring.fetch_itip_object_status(" . json_serialize($metadata) . ")", 'docready');
 
         // get localized texts from the right domain
-        foreach (array('savingdata','deleteobjectconfirm','declinedeleteconfirm','declineattendee','declineattendeeconfirm','cancel') as $label) {
+        foreach (array('savingdata','deleteobjectconfirm','declinedeleteconfirm','declineattendee',
+            'cancel','itipdelegated','declineattendeeconfirm','itipcomment','delegateinvitation',
+            'delegateto','delegatersvpme','delegateinvalidaddress') as $label) {
           $this->rc->output->command('add_label', "itip.$label", $this->gettext($label));
         }
 
@@ -570,6 +632,14 @@ class libcalendaring_itip
 
         $buttons .= html::div('itip-reply-controls', $this->itip_rsvp_options_ui($attrib['id']));
 
+        // add localized texts for the delegation dialog
+        if (in_array('delegated', $actions)) {
+            foreach (array('itipdelegated','itipcomment','delegateinvitation',
+                  'delegateto','delegatersvpme','delegateinvalidaddress') as $label) {
+                $this->rc->output->command('add_label', "itip.$label", $this->gettext($label));
+            }
+        }
+
         return html::div($attrib,
             html::div('label', $this->gettext('acceptinvitation')) .
             html::div('rsvp-buttons', $buttons));
diff --git a/plugins/libcalendaring/libcalendaring.js b/plugins/libcalendaring/libcalendaring.js
index 8bf9c356..bb5a66f9 100644
--- a/plugins/libcalendaring/libcalendaring.js
+++ b/plugins/libcalendaring/libcalendaring.js
@@ -803,6 +803,22 @@ rcube_libcalendaring.add_from_itip_mail = function(mime_id, task, status, dom_id
         del = confirm(rcmail.gettext('itip.declinedeleteconfirm'));
     }
 
+    // open dialog for iTip delegation
+    if (status == 'delegated') {
+        rcube_libcalendaring.itip_delegate_dialog(function(data) {
+            rcmail.http_post(task + '/itip-delegate', {
+                _uid: rcmail.env.uid,
+                _mbox: rcmail.env.mailbox,
+                _part: mime_id,
+                _to: data.to,
+                _rsvp: data.rsvp ? 1 : 0,
+                _comment: data.comment,
+                _folder: data.target
+            }, rcmail.set_busy(true, 'itip.savingdata'));
+        }, $('#rsvp-'+dom_id+' .folder-select'));
+        return false;
+    }
+
     var noreply = 0, comment = '';
     if (dom_id) {
       noreply = $('#noreply-'+dom_id+':checked').length ? 1 : 0;
@@ -824,6 +840,90 @@ rcube_libcalendaring.add_from_itip_mail = function(mime_id, task, status, dom_id
     return false;
 };
 
+/**
+ * Helper function to render the iTip delegation dialog
+ * and trigger a callback function when submitted.
+ */
+rcube_libcalendaring.itip_delegate_dialog = function(callback, selector)
+{
+    // show dialog for entering the delegatee address and comment
+    var html = '<form class="itip-dialog-form" action="javascript:void()">' +
+        '<div class="form-section">' +
+            '<label for="itip-delegate-to">' + rcmail.gettext('itip.delegateto') + '</label><br/>' +
+            '<input type="text" id="itip-delegate-to" class="text" size="40" value="" />' +
+        '</div>' +
+        '<div class="form-section">' +
+            '<label for="itip-delegate-rsvp">' +
+                '<input type="checkbox" id="itip-delegate-rsvp" class="checkbox" size="40" value="" />' +
+                rcmail.gettext('itip.delegatersvpme') +
+            '</label>' +
+        '</div>' +
+        '<div class="form-section">' +
+            '<textarea id="itip-delegate-comment" class="itip-comment" cols="40" rows="8" placeholder="' +
+                rcmail.gettext('itip.itipcomment') + '"></textarea>' + 
+        '</div>' +
+        '<div class="form-section">' +
+            (selector ? selector.html() : '') +
+        '</div>' +
+    '</form>';
+
+    var dialog, buttons = [];
+    buttons.push({
+        text: rcmail.gettext('itipdelegated', 'itip'),
+        click: function() {
+            var doc = window.parent.document,
+                delegatee = String($('#itip-delegate-to', doc).val()).replace(/(^\s+)|(\s+$)/, '');
+
+            if (delegatee != '' && rcube_check_email(delegatee, true)) {
+                callback({
+                    to: delegatee,
+                    rsvp: $('#itip-delegate-rsvp', doc).prop('checked'),
+                    comment: $('#itip-delegate-comment', doc).val(),
+                    target: $('#itip-saveto', doc).val()
+                });
+
+                setTimeout(function() { dialog.dialog("close"); }, 500);
+            }
+            else {
+                alert(rcmail.gettext('itip.delegateinvalidaddress'));
+                $('#itip-delegate-to', doc).focus();
+            }
+        }
+    });
+
+    buttons.push({
+        text: rcmail.gettext('cancel', 'itip'),
+        click: function() {
+            dialog.dialog('close');
+        }
+    });
+
+    dialog = rcmail.show_popup_dialog(html, rcmail.gettext('delegateinvitation', 'itip'), buttons, {
+        width: 460,
+        open: function(event, ui) {
+            $(this).parent().find('.ui-button:not(.ui-dialog-titlebar-close)').first().addClass('mainaction');
+            $(this).find('#itip-saveto').val('');
+
+            // initialize autocompletion
+            var ac_props, rcm = rcmail.is_framed() ? parent.rcmail : rcmail;
+            if (rcmail.env.autocomplete_threads > 0) {
+                ac_props = {
+                    threads: rcmail.env.autocomplete_threads,
+                    sources: rcmail.env.autocomplete_sources
+                };
+            }
+            rcm.init_address_input_events($(this).find('#itip-delegate-to').focus(), ac_props);
+            rcm.env.recipients_delimiter = '';
+        },
+        close: function(event, ui) {
+            rcmail.ksearch_blur();
+            $(this).remove();
+        }
+    });
+
+    return dialog;
+};
+
 /**
  *
  */
@@ -870,7 +970,7 @@ rcube_libcalendaring.decline_attendee_reply = function(mime_id, task)
     dialog = rcmail.show_popup_dialog(html, rcmail.gettext('declineattendee', 'itip'), buttons, {
         width: 460,
         open: function() {
-            $(this).parent().find('.ui-button').first().addClass('mainaction');
+            $(this).parent().find('.ui-button:not(.ui-dialog-titlebar-close)').first().addClass('mainaction');
             $('#itip-decline-comment').focus();
         }
     });
diff --git a/plugins/libcalendaring/localization/en_US.inc b/plugins/libcalendaring/localization/en_US.inc
index 9c3507cc..2542c47c 100644
--- a/plugins/libcalendaring/localization/en_US.inc
+++ b/plugins/libcalendaring/localization/en_US.inc
@@ -98,6 +98,8 @@ $labels['itipsubjectdeclined'] = '"$title" has been declined by $name';
 $labels['itipsubjectin-process'] = '"$title" is in-process by $name';
 $labels['itipsubjectcompleted'] = '"$title" was completed by $name';
 $labels['itipsubjectcancel'] = 'Your participation in "$title" has been cancelled';
+$labels['itipsubjectdelegated'] = '"$title" has been delegated by $name';
+$labels['itipsubjectdelegatedto'] = '"$title" has been delegated to you by $name';
 
 $labels['itipnewattendee'] = 'This is a reply from a new participant';
 $labels['updateattendeestatus'] = 'Update the participant\'s status';
@@ -139,6 +141,11 @@ $labels['openpreview'] = 'Open Preview';
 $labels['deleteobjectconfirm'] = 'Do you really want to delete this object?';
 $labels['declinedeleteconfirm'] = 'Do you also want to delete this declined object from your account?';
 
+$labels['delegateinvitation'] = 'Delegate Invitation';
+$labels['delegateto'] = 'Delegate to';
+$labels['delegatersvpme'] = 'Keep me informed about updates of this incidence';
+$labels['delegateinvalidaddress'] = 'Please enter a valid email address for the delegate';
+
 $labels['savingdata'] = 'Saving data...';
 
 // attendees labels
diff --git a/plugins/libcalendaring/skins/larry/libcal.css b/plugins/libcalendaring/skins/larry/libcal.css
index 89e123ff..f679abc3 100644
--- a/plugins/libcalendaring/skins/larry/libcal.css
+++ b/plugins/libcalendaring/skins/larry/libcal.css
@@ -156,3 +156,11 @@ label.noreply-toggle + a.reply-comment-toggle {
 	margin-top: -1.4em;
 }
 
+.itip-dialog-form input.text {
+	width: 98%;
+}
+
+.itip-dialog-form label > input.checkbox {
+	margin-left: 0;
+	margin-right: 10px;
+}