"Appointments, contacts, and tasks for the mailbox [Mailbox Name] couldn't be synchronized...The system will try again later" warning appears in Dynamics 365


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Exchange Error Message : The operation can't be performed because the item is out of date.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. 

More Info

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.

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