501 Your domain does not seem to be valid. Could not find MX record for your domain.
501 5.6.0 Data format error
Diagnostic-Code: SMTP; 501 Your domain does not seem to be valid. Could not find MX record for your domain.
Subject: Cron [ -x /usr/lib/php5/maxlifetime ] && [ -d /var/lib/php5 ] && find /var/lib/php5/ -depth -mindepth 1 -maxdepth 1 -type f -cmin +$(/usr/lib/php5/maxlifetime) -delete
Content-Type: text/plain; charset=ANSI_X3.4-1968
X-Cron-Env: <SHELL=/bin/sh>
X-Cron-Env: <HOME=/root>
X-Cron-Env: <PATH=/usr/bin:/bin>
X-Cron-Env: <LOGNAME=root>
the following error comes as mail every 30 min
please help
thanks in advance