How to check if your ISP blocks SMTP port 25 or 587

Please replace 'mail.domain.com' in the example below with your actual domain name. 

In Windows open a MS-DOS prompt or "command prompt" and type the following command: 'telnet mail.domain.com 25'

If the port is open you should see a SMTP banner.
If the port is blocked you will get a timeout or connection error.

For *nix based systems open your terminal and type: 'telnet mail.domain.com 25'

If Telnet is not installed on your Windows system you can follow these instructions.

Open Control Panel.
Click Programs and Features.
Click Turn Windows features on or off.
In the Windows Features dialog box, check the Telnet Client check box. Click OK.
The system installs the appropriate files. This will take a few seconds to a minute.

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