Symptoms
In Microsoft Outlook, you see duplicate folders in your Microsoft Exchange Server mailbox when you view the Outlook folder list, or when you view the folder list by using Outlook Web App (OWA).
Cause
A mobile device or a third-party server application that synchronizes with the Exchange Server mailbox may unexpectedly introduce the duplication. Or, the unexpected duplication may be the result of Exchange Server mailbox maintenance or of other changes that are performed on the computer that is running Exchange Server. Other factors could also contribute to the issue described in the Symptoms section of this article.
Solution
You need to disable automapping from EWS
Add-MailboxPermission -Identity “identityname” -User ‘username’ -AccessRight FullAccess -InheritanceType All -Automapping $false
