You cannot enable UM (Unified messaging) feature for users and get following errors.
Enable-UMMailbox -Identity <> -UMMailboxPolicy <> -Extensions <> -PinExpired:$true -SipResourceIdentifier <>
Mailbox <> couldn't be initialized for Unified Messaging: There was an error accessing the mailbox using EWS. The requested operation failed with ResponseCode "ErrorInternalServerError". Details : An internal server error occurred. The operation failed.
+ CategoryInfo : NotSpecified: (:) [Enable-UMMailbox], RecipientTaskException
Additionally you get following error while accessing the affected user's mailbox through OWA.
A problem occurred while you were trying to use your mailbox.
This happens due to corruption in the Search of user's mailbox so we need to follow below steps to resolve it.
>Need to configure affected user’s Outlook profile in ONLINE mode.
>Run the MFCMAPI Tool and navigate to Session->logon.
>Select affected user's ONLINE profile.
>Right Click on the user and click on Open Store.
>Expand Root Mailbox->Finder.
>Permanently delete all folders starting with string Search*.
>Log Out from MFCMAPI.
Note:- Deleting search folders will remove all search queries from user's mailbox.