I'm new to this VPS stuff. We had Debian 6 running with Postfix and Courier. That worked well, until I had to reinstall the server. Now the mail applications can't connect to mail.domain.com. I have tried the old setup, and now followed the Debian 7 how to Virtual Users And Domains With Postfix, Courier, MySQL And SquirrelMail (Debian Wheezy). I just keep getting the message that the server can't be contacted. I haven't changed the DNS settings, when I ping mail.domain.com, it gets a response. What am I doing wrong?