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Knowledge document #1122

No synchronization between Microsoft Outlook and Exchange Server

Microsoft Outlook cannot synchronize with a Microsoft Exchange Server using the FRITZ!Box's internet connection. This is the case with connections from a computer in the FRITZ!Box home network to an Exchange Server on the internet as well as connections from a computer on the internet to an Exchange Server in the home network.

Cause

  • Outlook uses UDP ports 137-139 to synchronize with an Exchange Server in certain configurations. Since these ports are frequently used to carry out attacks on Windows computers and they are normally not required for communication in the internet, the FRITZ!Box and some internet service providers (for example in the cable network) block access over these ports ("NetBIOS filter").

Configuring the Exchange Server for synchronization without NetBIOS

  1. Configure the Microsoft Exchange Server so that it does not use NetBIOS or the Windows Messenger Service for synchronization.
  2. If necessary, adjust the configuration of Microsoft Outlook.

    Note:You can find Information on the necessary settings in the Exchange Server or Outlook in the corresponding manual, or consult Microsoft directly.

Workaround

If the configuration of the Microsoft Exchange Server cannot be changed and the internet service provider does not block NetBIOS, you can disable the NetBIOS filter in the FRITZ!Box instead:

Important:When the NetBIOS filter is disabled, computers in the home network may be subject to more frequent attacks from the internet. Therefore, set up a firewall on all computers in the home network.

  1. Click "Internet" in the FRITZ!Box user interface.
  2. Click "Filter" in the "Internet" menu.
  3. Click on the "Lists" tab.
  4. Click "Global Filter Settings" to display all of the filter settings.
  5. Disable the option "NetBIOS filter enabled".
  6. Click "Apply" to save the settings.
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