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How to Tell if Your ISP Is Blocking Port 25

Sometimes, our customers use Earthnet for their email, but another ISP for their Internet connection, for example if DSL is not available in your area but you want to retain your Earthnet email address.

More and more ISPs decided to block port 25, which is the port that Earthnet uses to send out outgoing messages with If your ISP blocks port 25, you will NOT be able to use our outgoing mail server - - to send out messages. For example, if your ISP is Comcast, chances are you can't send messages using our mail server. You can still receive, but you can't send through Earthnet.

In that case, you will have to contact your ISP and ask them how to configure your email program to send out messages using their outgoing mail server. Alernately, use to send out emails on port 80.

Why do some ISPs block port 25? Because port 25 is the most widely used port for outgoing mail, and most spammers use that port to innundate the world with their spam. If that port is blocked by your ISP, spammers won't be able to use your computer to turn it into a spam launching base.

If you use a Windows computer:

1 - Click on the Start menu in the lower left-hand corner

2 - Click on the 'Run' icon

3 - In the little box that pops up, type in: cmd and press the Enter key. If it doesn't work, try typing command then press Enter.

4 - This should open a black DOS window.

5 - At the command prompt, type the following exactly as shown, followed by the Enter key:

telnet 25

6 - If your ISP does NOT block port 25, the screen will clear and you will see the following response:

220 ESMTP Postfix.

Type quit which will get you:

221 2.0.0 Bye
Connection to host lost.

If your ISP DOES BLOCK port 25, then you will see:

Connecting To not open connection to the host, on port 25: Connect failed

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If you use a Mac OS X computer

1 - Bring the terminal window. To do so, go to the finder, click on Applications, Utilities and finally Terminal:

2 - At the prompt sign, type the following exactly as follows, then press the Return key:

telnet 25

3 - If your ISP does NOT block port 25, you will see:

Connected to
Escape character is '^]'.
220 ESMTP Postfix

Type quit, which will show the following:

221 2.0.0 Bye
Connection closed by foreign host.

If your ISP DOES BLOCK port 25, you should see the following:

telnet: connect to address Connection refused
telnet: Unable to connect to remote host

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What now?

If you have found out that your port 25 is blocked, then you will need to make some adjustments to your outgoing mail server settings. Click here to find out how.

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