How to check if port 25 is blocked

If you're able to get email without any problems, but you're unable to send email from your chosen messaging client, and you're adamant that your outgoing mail server settings are correct you may be blocked by your ISP from connecting to the server on port 25.

The default port for SMTP (sending mail) is port 25. In some cases ISP's block access in order to eliminate the risk from spammers. In this case it can block you from being able to successfully connect to your mail server to send mail through your account. However, there are some cases where modems or routers also blocked port 25. The following article will help to explain how to check port 25, and what you can do if it is. 

How to run a check to see if port 25 is blocked.

This article explains how to see if port 25 is blocked. Follow the directions for the OS that you're using at the local level. 

Windows 7/8/10

Windows 98/XP/Vista

MacOS/OS X

  1. Click the Windows icon in the lower left or press the Windows key.
  2. Type cmd with the menu open.
  3. Press Enter or select Command Prompt (or cmd on Windows 7/8) with your mouse.
  4. Type cmd and Select Command Prompt from the Windows Menu.
  5. Install the telnet program by typing this into the  command prompt and pressing 
  6. Enter: pkgmgr /iu:”TelnetClient”
  7. Wait for few moments while telnet is installed.
  8. On Windows 7 and 8, you may need to close the command window and follow steps 1-3 above to reopen the command prompt. This step is not necessary in Windows 10.
  9. If you have problems installing telnet via the command prompt, you can navigate to Control Panels from the Windows menu, then find Programs and Features section and select Turn Windows Features On or Off. 
  10. Look for Telnet Client (not Telnet Server) and make sure the box next to it is checked and then click OK.
  11. Select Telnet Client from Windows Features and Click OK.
  12. Type telnet MAILSERVER 25 (replace MAILSERVER with your mail server (SMTP) which may be something like server.domain.com or mail.yourdomain.com).
  13. Type the Appropriate Command to Check if the Port is Open.
  14. Press Enter.
  15. If you aren't blocked, you will now see a connection notification from the remote mail server, which may look something like this:
  16. Example of a Successful Connection to a Mail Server via Telnet
  17. If that port is blocked, you will receive a connection error.

What to Do if Port 25 is Blocked

  1. Configure your mail client to use port 26 or port 587 for outgoing mail (SMTP) instead. This will usually do the trick.
  2. On a cPanel server, getting Exim to listen on another port is easy, just check Exim Mailserver on Another Port in the Service Manager feature in WHM and select the port to use (26 is the default), then save changes.
  3. Contact your ISP to confirm they are blocking port 25. You'll likely need to change the SMTP port (as in step 1 above) to get around this. ISPs rarely open closed ports for non-business internet clients.
  4. If your ISP says they are not blocking port 25 or 587 and you are still having problems sending mail, check your local router or cable modem to see if port 25 is blocked there.
  5. If nothing else works, and you have service with WebGo please contact us and we can investigate.
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