Telnet is a terminal emulation program that allows you from your computer to communicate directly with a remote computer.  Using Telnet is particularly useful when checking which email ports are opened and which are closed if you are having issues sending email.  For example if your Internet Service Provider has blocked Port 25 for outgoing mail, you can use Telnet to confirm the port is blocked.

By default, the Telnet command is turned off in Windows Vista and Windows 7.  To turn on Telnet, please read these instructions from the official Microsoft Windows website for enabling Telnet. Once Telnet has been enabled, open your command prompt.  Your command prompt can be found on your computer in the Accessories folder or by typing "CMD" in the Start Menu.  Your command prompt will look like this:


Now that you have your command prompt open, you can enter the command for Telnet.  The command follows this format:

  • telnet port#

For example, if for the domain we wanted to see if Port 25 was available, we would type in telnet 25 as seen here:


If Port 25 is open, then the following message will appear:


This means that email sent using Port 25 is not being blocked from your computer.  If you get a message that says "Connection Refused" or "No Route to Host" then your ISP or firewall setting is blocking the port, which is preventing you from sending email.  If 25 is blocked, you can also use port 587.

You can use telnet to check more then just the mail ports.  Here are the most common ports that you can check:

  • SMTP - 25, 587, and 465 (SSL)
  • POP3  - 110 and 995 (SSL)
  • IMAP - 143 and 993 (SSL)
  • MySQL - 3306
  • CPANEL - 2082 and 2083
  • Webmail - 2095 and 2096

If you are having trouble connecting to any of these services from one network but not from another network, the first thing to check it just to make sure the port for the program is not being blocked from the network.  If it is being blocked, then you can use an alternative port, or in some cases you may have to contact your ISP or company IT Department to have the port unblocked.

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