telnet command to check port access

telnet is a common tool used by sysadmins to check if a particular port is open or not on a remote server.

Sometimes you may have problems in sending or receiving emails.

The first step in troubleshooting the issue would be to first check the port access directly via telnet. Ports may be closed/blocked by say firewall on your local machine; or your internet service provider may block port 25.

And if that’s the case, you’ll never be able to use email on your PC using port 25.

How to use Telnet on Windows with CMD

Open a Command Prompt(CMD) Window
♦ Click on the Windows start menu and type “cmd” into the “Search programs and files” field. Hit enter key on your keyboard to run the program.

♦ A new black window will open. This where you enter the telnet command. The syntax of a telnet command consists of the following:

telnet server host name followed by portnumber (telnet server.example.com 25)
If the telnet process is complete, then you will see an output with the server hostname, server main IP address etc..

Telnet command can be used from linux as well as windows machines