Outlook Synchronization and preventing duplication of contacts, tasks, etc.

When a new contact is created in Dynamics NAV, you may want to synchronize that contact to Outlook. Sometimes it could happen that during the next synchronization attempt, this specific contact seems to duplicate somehow. This blog describe how this could happen and what you could do to prevent this. This blog will also describe how the synchronization works in detail. A future blog will describe what to do when this situation has occurred.

If you create a new contact in Dynamics NAV and synchronize that contact to Outlook via a normal synchronization, then a new contact will be created in the dedicated Outlook Synchronization folder in Outlook. Dynamics NAV must know that this process finished successfully, so what happens next is that a Unique Identifier is sent back from Outlook to Dynamics NAV. This Unique Identifier is stored in table 5302.

When the contact is created in Outlook but the Unique Identifier is not sent back to Dynamics NAV, during the next synchronization attempt, a duplication could occur.

Most of the time, this happens when the user does not know the synchronization is running in the background.


  • switching off the “Show synchronization progress” option in the Outlook Add-In that shows the synchronization is running
  • switching off the “Show synchronization summary” option after a successful synchronization
  • enabling the “Schedule automatic synchronization every” option

NOTE: using the “Schedule automatic synchronization every” in general is a bad idea because with a scheduled synchronization and with the current Outlook Synchronization solution, the progress bar and summary window will not be shown to the Outlook Synchronization user in Outlook!


With Office 2010 it is very easy to close Outlook –even when the synchronization is running! If the Unique Identifier is not sent back to Dynamics NAV, a previous attempt to synchronize new items to Outlook and the other way around will duplicate the synchronized data in Dynamics NAV or Outlook! The same scenario applies if the Outlook Synchronization User uses a laptop and closes the lid of the laptop (when he does not know the synchronization is running). Of course, this scenario could also happen if Outlook suddenly crashes; e.g. during a power failure, etc.

There are many reason why a duplication could occur, but in general an Outlook Synchronization User should know that the Outlook Add-In is running in the background and therefore, we now do not recommend to disable the “Show synchronization progress” option and the “Show synchronization summary” option. Enabling these options again would prevent the most common cause why a duplication could occur.


Marco Mels

This posting is provided "AS IS" with no warranties, and confers no rights