add healthcheck for postfix

core/postfix/health.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+
+if [ "$(echo QUIT|nc localhost 25|tail -n1|cut -f1 -d ' ')" = "221" ]; then
+	echo "ping successful"
+else
+	echo "ping failed"
+	exit 1
+fi