My Debian server is located in a datacenter and the system ports for smtp, ssh, ftp, pop3, http are monitored. When one of these processes is down, I will receive a sms on my mobile phone. According my ISPConfig hosting-controlpanel everything is functioning fine. And I do not have any problems with any of the running processes but … everytime I receive a message from datacenter that my smtp is down. Two minutes later or so, I receive a sms again that all running processes are running and that my server is fine. This happens again and again. I have contacted the company in the datacenter, and they told me that when my smtp-server is not showing the initial greeting within 20 seconds, the monitoring system thinks that my smtp-server is down. I think it has something to do with a setting within Postfix, I had a look at this problem, but it is not clear to me why this problem occurs. Can anyone give me advise? I would be very grateful.