Introduction

This article shows you how to troubleshoot SMTP connection issue using a telnet utility from your PC. The standard port used for SMTP connection to our servers is port 25 (some ISPs also open 587 as alternative SMTP port). Most often the reason for failed email sending is that your local Internet service provider blocks this port to prevent SPAM/BULK messages being sent from their networks.

How to run port 25 check in a Windows O/S?

If you're using Windows Vista or Windows 7, you must install the telnet first. Below is the steps to install it :

  • Open the Programs and Features Control Panel applet (Start -> Control Panel -> Programs and Features).

  • Click Turn Windows features on or off.

  • Tick Telnet Client and click OK.
    A dialog box will appear, 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.


Please click on the Start menu button, usually located on the left low corner of the screen. There is a tab called Run (In Windows 7, you can just search for "cmd" from the search menu after you click Windows icon). 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:

telnet smtp.example.com 25

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

220 smtp.example.com ESMTP

If you get a message saying that the connection is refused, this could be that your ISP is blocking the port 25 or your antivirus/firewall that has blocked the connection. The solution is that you can change the port settings to 587 on your email client software. If you are a VPS or Dedicated owner, you can contact our support to check how to enable the SMTP submissions port (587) on the server side.