I dont have knowledge on linux and how can i know which mail server is running on my linux box? Postfix/Exim? Btw Didn't found postfix folder in etc/, where can i find master.cf? .Any idea for modify cPPOP?
Easiest way might be to get the PID of what's listening on port 25:
# sudo lsof -i :25 COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME master 5664 root 12u IPv4 13732 TCP *:smtp (LISTEN)
Then find out what that process is:
# ps p 5664 PID TTY STAT TIME COMMAND 5664 ? Ss 0:12 /usr/lib/postfix/master
And I'm running postfix. For sendmail, it looks like this:
# lsof -i :25 COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME sendmail 3445 root 4u IPv4 12922 TCP localhost.localdomain:smtp (LISTEN)
Postfix config is under /etc/postfix , "sudo" might be necessary