diff --git a/plugins/calendar/calendar.php b/plugins/calendar/calendar.php
index 9bf68c78..63bfe11e 100644
--- a/plugins/calendar/calendar.php
+++ b/plugins/calendar/calendar.php
@@ -747,10 +747,12 @@ class calendar extends rcube_plugin
               $organizer = $attendee;
             else if ($attendee['email'] && in_array(strtolower($attendee['email']), $emails)) {
               $old['attendees'][$i]['status'] = 'DECLINED';
+              $reply_sender = $attendee['email'];
             }
           }
           
           $itip = $this->load_itip();
+          $itip->set_sender_email($reply_sender);
           if ($organizer && $itip->send_itip_message($old, 'REPLY', $organizer, 'itipsubjectdeclined', 'itipmailbodydeclined'))
             $this->rc->output->command('display_message', $this->gettext(array('name' => 'sentresponseto', 'vars' => array('mailto' => $organizer['name'] ? $organizer['name'] : $organizer['email']))), 'confirmation');
           else
@@ -1953,6 +1955,7 @@ class calendar extends rcube_plugin
           }
           else if ($attendee['email'] && in_array(strtolower($attendee['email']), $emails)) {
             $event['attendees'][$i]['status'] = strtoupper($status);
+            $reply_sender = $attendee['email'];
           }
         }
       }
@@ -2037,6 +2040,7 @@ class calendar extends rcube_plugin
     // send iTip reply
     if ($this->ical->method == 'REQUEST' && $organizer && !in_array(strtolower($organizer['email']), $emails) && !$error_msg) {
       $itip = $this->load_itip();
+      $itip->set_sender_email($reply_sender);
       if ($itip->send_itip_message($event, 'REPLY', $organizer, 'itipsubject' . $status, 'itipmailbody' . $status))
         $this->rc->output->command('display_message', $this->gettext(array('name' => 'sentresponseto', 'vars' => array('mailto' => $organizer['name'] ? $organizer['name'] : $organizer['email']))), 'confirmation');
       else
diff --git a/plugins/calendar/lib/calendar_itip.php b/plugins/calendar/lib/calendar_itip.php
index 30fb8128..51a1c92b 100644
--- a/plugins/calendar/lib/calendar_itip.php
+++ b/plugins/calendar/lib/calendar_itip.php
@@ -40,6 +40,12 @@ class calendar_itip
     $this->cal->add_hook('smtp_connect', array($this, 'smtp_connect_hook'));
   }
 
+  function set_sender_email($email)
+  {
+    if (!empty($email))
+      $this->sender['email'] = $email;
+  }
+
   /**
    * Send an iTip mail message
    *
@@ -135,8 +141,27 @@ class calendar_itip
   public function compose_itip_message($event, $method)
   {
     $from = rcube_idn_to_ascii($this->sender['email']);
+    $from_utf = rcube_idn_to_utf8($from);
     $sender = format_email_recipient($from, $this->sender['name']);
     
+    // truncate list attendees down to the recipient of the iTip Reply.
+    // constraints for a METHOD:REPLY according to RFC 5546
+    if ($method == 'REPLY') {
+      $replying_attendee = null; $reply_attendees = array();
+      foreach ($event['attendees'] as $attendee) {
+        if ($attendee['role'] == 'ORGANIZER') {
+          $reply_attendees[] = $attendee;
+        }
+        else if (strcasecmp($attedee['email'], $from) == 0 || strcasecmp($attendee['email'], $from_utf) == 0) {
+          $replying_attendee = $attendee;
+        }
+      }
+      if ($replying_attendee) {
+        $reply_attendees[] = $replying_attendee;
+        $event['attendees'] = $reply_attendees;
+      }
+    }
+    
     // compose multipart message using PEAR:Mail_Mime
     $message = new Mail_mime("\r\n");
     $message->setParam('text_encoding', 'quoted-printable');