A few ideas to help you track down...
- Have a check see if postfix is actually running. Do something like "ps ax | grep master" - you should have a process listed there.
See if its listening on the address you're connecting to - "netstat -A inet -nlp" see if a process "master" for port 25 is listening on either any address (0.0.0.0) or a specified address.
- Check you're not firewalled out at all?
- On my ubuntu installation when I configured postfix it automatically specified start on boot. You might like to check thats the case on yours.
- Where are you telneting from? Is it your local PC, could it be antivirus or similar getting in the way?
- Maybe do a "service postfix restart" to check its starting correctly.
- Have a look in the mail log file for errors - something like "cat /var/log/mail.log".
- you said you followed a Perfect Server guide, suggesting you installed ISPConfig. What happens when you log in there and go to the monitor tab? Does it show any services offline?