diff --git a/server/lib/classes/monitor_tools.inc.php b/server/lib/classes/monitor_tools.inc.php
index 7d879c4647c9b1fa8e9d42d8fc9cca9050c3e28e..4761d96727f67e019d32917093d842dca420d5ba 100644
--- a/server/lib/classes/monitor_tools.inc.php
+++ b/server/lib/classes/monitor_tools.inc.php
@@ -177,7 +177,7 @@ class monitor_tools {
 					unset($quotafile);
 				} else {
 					exec('du -s '.escapeshellcmd($filename),$out);
-					$parts = explode(' ',$out);
+					$parts = explode(' ',$out[0]);
 					$data[$email]['used'] = intval($parts[0])*1024;
 					unset($out);
 					unset($parts);
diff --git a/server/mods-available/monitor_core_module.inc.php b/server/mods-available/monitor_core_module.inc.php
index ca1e9e44e56fc6d9d4fb34c809cae14cacc9b9e6..bfb03be975dbd5c390a709104902dd0b0de4d002 100644
--- a/server/mods-available/monitor_core_module.inc.php
+++ b/server/mods-available/monitor_core_module.inc.php
@@ -120,6 +120,13 @@ class monitor_core_module {
         global $app;
 
         /*
+		 *  This monitoring is expensive, so do it only every 15 minutes
+		 */
+		$min = @date('i');
+		if ($min % 15 != 0) return;
+		
+		
+		/*
          * First we get the Monitoring-data from the tools
          */
         $res = $this->_tools->monitorEmailQuota();