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Good Ol Fashion Telnet

It’s not uncommon to hear that someone has no problem receiving email but lacks the ability to send out. To later learn this is a site wide issue it’s likely something on the network is causing the problem. To further pin point the issueof the errors being returned, Exchange Management Console (EMC) offers an intuitive queue viewer allowing you to view which messages are not being sent out. This can be accessed through the 2010 EMC by following these steps,

  1. In the console tree, click Toolbox.
  2. In the result pane, click Queue Viewer.
  3. In the action pane, click Open Tool.
  4. In Queue Viewer, click the Queues tab. A list of all queues on the server to which you’re connected is displayed.

The queue viewer will notify you of any messages that are currently stuckrepeatedly attempting to send outbound. Fortunately there are more tools thatwill allow you to diagnose the issue further and assist in troubleshooting,Telnet being one of them. Telnet is an extremely useful tool fortroubleshooting issues related to mail flow. Telnet can be used to test thefollowing:

  • Ensure that your server isaccessible over the Internet. 
  • Attempt mail delivery directly over the TCP port.
  • Determine that all servers are accepting connections.
  • Determine if a firewall is blocking a connection.
  • Ensure that a single user can receive mail.

  • Ensure that a specific domain can receive mail.

  • Ensure that a specific user or domain can send mail to your domain

At any rate, with this apparent issue of outbound mail hanging, Telnet can be used to test a port 25 connection from a server to server or from a workstation to server.

  1. Openan CMD prompt, and enter this command:
    • telnet mail.contoso.com 25 [Enter]
  2. This will open a Telnet window, and within a short time, you will be connected to the SMTP server.
  3. Now the server expects you to identify yourself. If you have a domain-name, then you should enter the domain-name here. Preceded with a mail statement.
    • Helo mail.contoso.com [Enter]
  4. Next give the server your e-mail address. Note that most SMTP servers require that your e-mail address belong to the same domain as the server
  5. Tell the server who you want to send the e-mail to.
  6. You have told the server your e-mail address, and the recipient’s e-mail address, so now you can go ahead and type the subject of the e-mail. You have to do that with the data command:
    • Data [Enter]
  7. Next, fill the command prompt with what you want the email to say.
    • This is a test e-mail. Remember to type it all right. Backspace key doesn’t work in Telnet. If you make a mistake, you will need to start all over. [Enter]
  8. Make sure, that once you have completed your email you input a period ‘.’ And the hit [Enter] to send the email.

At this point one of two things can happen; either the email is sent successfully or errors out.Telnet happens to be quite descriptive in the errors associated with SMTP.These errors are extremely useful in diagnosing the issue at hand. In a nutshell, Telnet allows the test of SMTP connection from a server or workstation to create a connection to a mail server and verify that port 25 is operational.

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