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Images in Outlook Suddenly Stopped Working after TMG reboot

    Question

  • Hello

    I have a TMG server which filters all the outgoing traffic and also handles incomming traffic.

    The TMG server is set as the gateway for DHCP clients and the proxy is also applied in IE.

    Everything was working ok until the TMG server installed some updates and rebooted. Now for some reason in HTML emails all images are getting blocked. On the client it doesn't seem to matter if the proxy in IE is in or out and the gateway is set to the TMG server or the router (to bypass TMG).

    Normally Outlook would say "Right-click here to download pictures..." then you would right-click and tell it to show them and they would appear but now after telling it to show them it justs sits there for a few minutes trying to download then and then eventually it says "The linked image cannot be displayed..."

    Looking in the TMG log it says:

    Failed Connection Attempt

    Log type: Web Proxy (Forward)

    Status: 10054 An existing connection was forcibly closed by the remote host.

    Rule: Allow Web Access for All Users

    Source: Internal (192.168.5.8:65513)

    Destination: External (xxx.xxx.xxx.xxx:80)

    Request: GET http://www....

    Protocol: http

    User: anonymous

    I did search before posting this but the other topic about images in Outlook seems to be a different problem to mine.

    Please can anyone tell me what might have gone wrong or what I can check? Everything else and all other rules seem to still work correctly. The TMG server runs on Hyper-V and has 6 virtual NICS with one on the internal network and 5 on the external network.

    Thanks

    Robin

    P.S. When I came onto the server to troubleshoot the problem and looked at the alerts tab it told me that a certificate was close to expiry so I went through the listeners and re-applied the correct certificate and reset the error and it has not returned since.


    Robin Wilson

    Sunday, July 01, 2012 10:53 AM

Answers

  • This issue now seems to have fixed itself!

    Now images in Outlook are working normally on the clients even though nothing has changed.

    Very strange but glad it's resolved itself.

    I would be interested in any comments though in case it happens again in the future (as I don't know what caused it).

    Looking at the logs it was definately TMG blocking the traffic but now it has stopped. Very strange!

    Robin


    Robin Wilson

    • Marked as answer by robinwilson16 Sunday, July 01, 2012 7:14 PM
    Sunday, July 01, 2012 7:14 PM
  • I think I have now worked out the reason behind this.

    I have been having intermittent faults with the internet connection and it seems that TMG ends up directing requests for external sites to 192.168.1.1 which is the router (I can tell if I ping the location which didn't work). As TMG expects the request to be external it fails with the error above as well as logging IP spoofing attacks.

    Then when the internet connection is restored it seems to take TMG a while to update its DNS cache so eventually the images in the emails start working again. It's strange it doesn't seem to occur when browsing the internet using the web proxy.

    Robin


    Robin Wilson

    • Marked as answer by robinwilson16 Monday, July 02, 2012 6:55 PM
    Monday, July 02, 2012 6:55 PM

All replies

  • This issue now seems to have fixed itself!

    Now images in Outlook are working normally on the clients even though nothing has changed.

    Very strange but glad it's resolved itself.

    I would be interested in any comments though in case it happens again in the future (as I don't know what caused it).

    Looking at the logs it was definately TMG blocking the traffic but now it has stopped. Very strange!

    Robin


    Robin Wilson

    • Marked as answer by robinwilson16 Sunday, July 01, 2012 7:14 PM
    Sunday, July 01, 2012 7:14 PM
  • I think I have now worked out the reason behind this.

    I have been having intermittent faults with the internet connection and it seems that TMG ends up directing requests for external sites to 192.168.1.1 which is the router (I can tell if I ping the location which didn't work). As TMG expects the request to be external it fails with the error above as well as logging IP spoofing attacks.

    Then when the internet connection is restored it seems to take TMG a while to update its DNS cache so eventually the images in the emails start working again. It's strange it doesn't seem to occur when browsing the internet using the web proxy.

    Robin


    Robin Wilson

    • Marked as answer by robinwilson16 Monday, July 02, 2012 6:55 PM
    Monday, July 02, 2012 6:55 PM