Troubleshoot POP3 Mail Server with Telnet

I am finally getting an opportunity to write a post. I have been so busy with upgrades lately and had to put off writing for awhile.

The other day I had a number of users complaining about not being able to fetch mail to their mail client, MS Outlook. As usual, I attempted to duplicate the error. The error message was reporting unable to connect to the mail server. At that point, I decided to telnet the Post Office Protocol or POP3 port, 110, via the command line interface. Sure enough, I had a problem.

Note: The “before and after” command line examples are only for illustration purposes.

# telnet server 110
Trying 192.1xx.xx.xxx...
telnet: Unable to connect to remote host: Connection refused

I started thinking there was a problem with the inetd.conf file. After reviewing the file, I noticed the pop3 service was commented out. The appropriate change was made and inetd was restarted. Problem resolved.

# telnet server 110
Trying 192.1xx.xx.xxx...
Connected to server.
Escape character is '^]'.
+OK connected to pop3 on 3429

By the way, you can check out other popular port services, too.
# telnet server 6667
# telnet server 25