When viewing Alerts for a mailbox in Dynamics 365, you see the following warning:
"Appointments, contacts, and tasks for the mailbox [Mailbox Name] couldn't be synchronized. The owner of the associated email server profile [Profile Name] has been notified. The system will try again later."
The following additional details are also included:
"Error : Exchange Error Code: ErrorIrresolvableConflict
Exchange Error Message : The operation can't be performed because the item is out of date. Reload the item and try again. Exchange Error Details: System.Collections.Generic.Dictionary`2[System.String,System.String]"
This warning may appear if Server-Side Sync attempted to update an item in Microsoft Exchange and an ErrorIrresolvableConflict message was returned by the Exchange server. This is typically a temporary issue and the item will be updated successfully during the next synchronization cycle.
For additional information on Microsoft Exchange error codes such as ErrorIrresolvableConflict, refer to the following page:
If this message does not persist on the next synchronization cycle (typically 15 minutes), this warning can be ignored. If this message persists, you can contact Microsoft Support.