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How to check if port 25 is blocked

The standard port used for SMTP connection is 25. The most common reason for not being able to send messages is that your Internet service provider blocks this port due to spam. That's why we recommend using the alternative port 587 for your email SMTP connection. Although your ISP can also block that port. If that is the case you must use your ISP SMTP service to send emails.

If you are using Vista you probably have to install telnet. Just follow these instructions:

1. Open the Programs and Features Control Panel applet (Start, Control Panel, Programs and Features).
2. Select "Turn Windows features on or off."
3. Select the Telnet Client option and click OK.
4. A dialog box appears, confirming the installation of new features. After installation is complete, close the main Programs and Features Control Panel applet. The telnet command should now be available.

Here's how to, depending on your OS, check whether your ISP blocks port 25:

* Check port 25 with a Windows OS

Click on the Start menu button, usually located on the left low corner of the screen. There is a tab called "Run". You have to click on it, in order to proceed further. You will notice the appearance of a new small window on the screen. In the text field of this window you need to type "cmd" and then press the "Enter" key. Another window will open. It is the so called "MS-DOS prompt" or "command prompt". Just type the following command in the command prompt window and press "Enter":

telnet my-domain-name.com 25

* Check port 25 with Apple/Mac

Each Mac OS is delivered with a preinstalled terminal emulator. The terminal is a tool which allows you to execute commands from the command line. Usually, the terminal is located under your Mac HD -> "Applications" directory -> Utilities sub-directory. When the window opens, you will see a command line with a flashing cursor on it so you can start typing right away. Just type the following command and press "Enter":

telnet my-domain-name.com 25

* Check port 25 with Linux

Open your favorite terminal emulator and execute the following command in order to telnet your website:

telnet my-domain-name.com 25

Results from the 25 port check

If the test is successful, you should receive a message like this:

220-serv01.test.com ESMTP Exim 4.63 #1 Wed, 18 Apr 2008 07:17:30 -0500

If you get a message saying that the connection is refused you know the port is blocked and you need to use your own ISP such as smtp.yahoo.att.net (example for att).