diff --git a/apps/kolab_guam/src/rules/kolab_guam_rule_filter_groupware.erl b/apps/kolab_guam/src/rules/kolab_guam_rule_filter_groupware.erl
--- a/apps/kolab_guam/src/rules/kolab_guam_rule_filter_groupware.erl
+++ b/apps/kolab_guam/src/rules/kolab_guam_rule_filter_groupware.erl
@@ -65,14 +65,14 @@
 fetch_metadata(_ImapSession, _State) -> ok.
 
 apply_if_id_matches(<<"ID">>, Data, _State) ->
-    apply_if_found_kolab(binary:match(Data, <<"/Kolab">>));
+    apply_if_found_kolab(string:str(string:to_lower(binary_to_list(Data)), "/kolab"));
 apply_if_id_matches(Command, Data, State) ->
     case is_triggering_command(Command, Data, State) of
         true -> true;
         _ -> notyet
     end.
 
-apply_if_found_kolab(nomatch) -> true;
+apply_if_found_kolab(0) -> true;
 apply_if_found_kolab(_) -> false.
 
 filter_folders(<<>>, State) ->