Index: /trunk/roundcubemail/program/include/main.inc
===================================================================
--- /trunk/roundcubemail/program/include/main.inc	(revision 3103)
+++ /trunk/roundcubemail/program/include/main.inc	(revision 3104)
@@ -1414,5 +1414,5 @@
   global $RCMAIL;
   
-  if (isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] != 'off')
+  if (!empty($_SERVER['HTTPS']) && strtolower($_SERVER['HTTPS']) != 'off')
     return true;
   if ($port && $_SERVER['SERVER_PORT'] == $port)