FRITZ!Box 7390 Service - Knowledge Base

FRITZ!Box 7390 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.

Note:All instructions on configuration and settings given in this guide refer to the latest FRITZ!OS for the FRITZ!Box.

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.