How to check if port 25 is blocked? Print

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The standard port that is used to connect to the SMTP protocol is port 25. One of the most likely and common causes of errors when trying to send mail is blocking of port 25 by the Internet provider. In this situation there are two options. The first is to use a VPN, the second is to use an alternative port.

To check whether port 25 is blocked by your Internet provider, run the following command:


Start -> All programs -> Accessories -> Run -> cmd -> telnet 25

In English:

Start -> All programs -> Basic -> Run -> cmd -> telnet 25



Mac HD -> “Applications” directory -> Utilities sub-directory telnet 25



Open a terminal and enter the command:

telnet 25

Test results:

If port 25 is open, you will see a similar message with the server response:

220 ESMTP Postfix


If such a message does not appear, but you see a connection error message, the port is blocked!

Why is port 25 blocked? Most Internet providers block port 25 because it is used to send spam messages.

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