diff --git a/data/Dockerfiles/watchdog/watchdog.sh b/data/Dockerfiles/watchdog/watchdog.sh
index fbef6893..a76d5d9c 100755
--- a/data/Dockerfiles/watchdog/watchdog.sh
+++ b/data/Dockerfiles/watchdog/watchdog.sh
@@ -245,7 +245,7 @@ postfix_checks() {
     touch /tmp/postfix-mailcow; echo "$(tail -50 /tmp/postfix-mailcow)" > /tmp/postfix-mailcow
     host_ip=$(get_container_ip postfix-mailcow)
     err_c_cur=${err_count}
-    /usr/lib/nagios/plugins/check_smtp -4 -H ${host_ip} -p 589 -f "watchdog@invalid" -C "RCPT TO:null@localhost" -C DATA -C . -R 250 2>> /tmp/postfix-mailcow 1>&2; err_count=$(( ${err_count} + $? ))
+    /usr/lib/nagios/plugins/check_smtp -4 -H ${host_ip} -p 589 -f "watchdog@invalid" -C "RCPT TO:watchdog@localhost" -C DATA -C . -R 250 2>> /tmp/postfix-mailcow 1>&2; err_count=$(( ${err_count} + $? ))
     /usr/lib/nagios/plugins/check_smtp -4 -H ${host_ip} -p 589 -S 2>> /tmp/postfix-mailcow 1>&2; err_count=$(( ${err_count} + $? ))
     [ ${err_c_cur} -eq ${err_count} ] && [ ! $((${err_count} - 1)) -lt 0 ] && err_count=$((${err_count} - 1)) diff_c=1
     [ ${err_c_cur} -ne ${err_count} ] && diff_c=$(( ${err_c_cur} - ${err_count} ))