How to tell if SMTP standard port 25 is blocked


The standard port used for SMTP ( Outgoing Email ) connections is 25. One of the most common reasons for not being able to send email is that your ISP (Internet Service Provider) blocks this port.

The reason that most ISP's block the port 25 is because it is often used by malware to send SPAM (Unsolicited Email).

FatCat Servers use an alternative SMTP port 26 to work around this issue, use of this port is highly recommended. Information on how to change the SMTP port for the most popular mail clients can be found in our Email tutorials.

Here's how to check whether your ISP blocks port 25:

Check port 25 in Windows

Click on the Start menu button, usually located at the lower left corner of the screen.

There is a tab called "Run". Click it and a new window will pop up.

In the text field of this window you need to type cmd and then press the "Enter" key. A "command prompt" will open.

Type the following command in the command prompt window and press "Enter": telnet 25

NOTE: For Vista or Windows 7 you may have to install telnet, type pkgmgr /iu:"TelnetClient" at command prompt then hit "enter"

Check port 25 in Mac OS

Mac OS has a preinstalled terminal emulator usually it is located under your Mac HD -> "Applications" directory -> Utilities sub-directory.

When the window opens, you will see a command line with a flashing cursor, type the following command and press "Enter": telnet 25

Check port 25 in Linux

Open your favorite terminal emulator and execute the following command in order to check the connection on port 25 to your domain: telnet 25

Understanding Results from the 25 port check

If the test is successful, you should receive a message similar to this one: ESMTP Exim 4.80 #2 Fri, 19 Oct 2012 14:52:04 -0400

220-We do not authorize the use of this system to transport unsolicited,

220 and/or bulk e-mail.

and you should be able to use port 25 or 26

If the test is un-successful, you should receive a message similar to this one:

Connecting To not open connection to the host

, on port 25: Connect failed

and you must use port 26