FRITZ!Box 4040 Service - Knowledge Base

FRITZ!Box 4040 Service

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 in the internet as well as connections from a computer in the internet to an Exchange Server in the home network.


  • In certain configurations, Outlook uses UDP ports 137-139 for synchronizing with an Exchange Server. The FRITZ!Box blocks these ports ("NetBIOS Filter") since they are often used to attack Windows computers and they are normally not required for communication in the internet.

1 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.


If you cannot or do not want to change the configuration of the Microsoft Exchange Server or Microsoft Outlook, disable the NetBIOS filter in the FRITZ!Box:

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 "Filters" in the "Internet" menu.
  3. Click on the "Lists" tab.
  4. Disable the option "NetBIOS filter enabled". If the option is not displayed, enable the Advanced View first.
  5. Click "Apply" to save the settings.

2 Disabling the "Navigationshilfe" from the German Telekom

If you are a German Telekom customer, the problem may be caused by the so-called Navigationshilfe (navigation help) from the German Telekom. If you are using the FRITZ!Box on an internet connection from the Telekom, disable the "Navigationshilfe" for testing purposes:

  1. Log into the Telekom "Kundencenter" (customer center).
  2. Disable the "Navigationshilfe" in the Telekom Kundencenter.
  3. Restart the FRITZ!Box by unplugging it briefly and then plug it back in again after a few seconds.