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Introduction
One of the common issues we encounter in our support department is that customers who are traveling have problems sending email. Often, this is due to connecting to a new network that has not been used before for sending emails, such as open wireless networks in cafes, libraries, or other public locations.

Every network has its own rules, and sometimes, there are rules regarding which outbound email servers (SMTP) you are allowed to connect to and use.
The main reason for such rules is to protect the network from being labeled as a source of spam (junk email). Spammers are traced by their IP addresses, which can harm the reputation of the network they are using to connect to the internet.

By limiting SMTP connections on a network to a single acceptable SMTP server, the network can be more tightly controlled and protected from being flagged as a spam source. These changes can often be applied suddenly and without warning to users on the affected network.

Testing SMTP Connection with Telnet
If you're facing issues sending email from a home or work network, you can use the following commands to test your connection to your usual SMTP server.

How to Use Telnet in Windows to Test SMTP Service

Note: Enabling Telnet in Windows
If you're using Windows Vista or Windows 7, you might need to enable the Telnet client before following the instructions below. If you're unable to run Telnet from the command prompt, you should follow these extra steps:

1. Click on "Start."

2. Click on "Control Panel."

3. Click on "Programs and Features."

4. Click on "Turn Windows Features On or Off."

5. Check the box next to "Telnet Client" and click "OK."

Once you've done this, you should be able to run the Telnet command from the command prompt.

Steps to Use Telnet to Test SMTP Connection:

1. Open the "Start" menu and select "Run."

2. In the "Run" box, type "command" and press "Enter." (You can also use "cmd" in many versions of Windows.) This will open a command prompt window.

Type the following command:

• Replace your_smtp_server.com with the SMTP server address you want to test. This is typically the address used by your email provider (e.g., smtp.gmail.com or smtp.mail.yahoo.com).

Note:

• If the connection is successful, you'll see a response from the server in the command prompt window, indicating that the Telnet connection to the SMTP server was successful.

• If you see error messages such as "Connection Timed Out" or "Could Not Connect," this indicates that there is an issue connecting to the server, potentially due to network rules or server configuration issues.

Test SMTP Server Using Telnet:

Once you’ve successfully connected, you can start issuing SMTP commands to test the service. For example:

1. HELO Command:

   • Type:

     HELO yourdomain.com

   • If the response is good, the server will reply with something like:

     250 Hello yourdomain.com

2. MAIL FROM Command:

   • Type:

     MAIL FROM: <youremail@yourdomain.com>

   • The server will respond in kind if it’s working correctly.

3. RCPT TO Command:

   • Type:

     RCPT TO: <recipientemail@domain.com>

4. DATA Command:

   • Type:

     DATA

   • You can then proceed to add the body of your email.

Additional Tips:

• If you're unable to connect to the SMTP server, try using another port number such as 587 or 465, as some networks may block port 25.

• Check your firewall settings or your Internet Service Provider's (ISP) policies, which may be blocking certain ports.