The sync monitor repair process includes the following steps: Registry value options are added to enable control of the repair process steps.Diagnostic logging is added to help the Outlook product team understand future problems in this area.The algorithm for detecting folders that are out-of-sync is adjusted to be less aggressive.The October 4, 2016, updates for Outlook 2016 and Outlook 2013 add the following important changes to the sync monitor logic: If the folder contents are large, this can also create unexpected network traffic and a poor user experience while you wait for the full re-sync of the folder to finish. This can cause an unexpected re-sync of a folder. If the repair on these folders cannot be successfully completed by using one of the non-intrusive steps, a full folder re-sync will eventually be scheduled. In this case, folders that are in a good sync state are incorrectly identified as broken. Sometimes, the original problem detection logic that is used by the sync monitor is too aggressive. If all other repairs fail, the sync monitor schedules a full re-sync of the folder. The steps are performed in order from least-intrusive to most-intrusive. The repair process is a series of steps that try to restore the sync state of the folders. If the number of items in each group do not match, a repair is necessary. For example, the sync monitor checks the unread items in the local copy of a folder, and then compares those items to the unread items in the server copy of the folder. The sync monitor runs a series of detection and repair actions based on the synchronization state health of every folder.

To enable this new functionality, see the registry information that is provided in the More Information section. By default, this updated detection and repair logic is not enabled.

Outlook 2016 sync issues in windows 10