In Microsoft Office 365 dedicated/ITAR, a user may experience one or more of the following issues when the Exchange Web Services (EWS) protocol for his or her mailbox is disabled:

  • The user doesn't obtain Free/Busy information by using a Microsoft Outlook client.

  • The user can't obtain or set Out of Office (OOF) information by using an Outlook client.

  • The user receives repeated credential prompts when he or she uses a Microsoft Lync client.

  • Lync conversation history isn't saved to the user's Microsoft Exchange Server mailbox.

  • Outlook/Lync presence integration doesn't work as expected.


This issue occurs when the EWSEnabled parameter of the user's Client Access Server (CAS) mailbox is set to FALSE. In this case, the user is prevented from accessing the EWS virtual directory on the Exchange server. Generally, the user receives an HTTP 403 (forbidden) error. 


To resolve this issue, set the EWSEnabled parameter to TRUE to let the user use the EWS protocol. To do this, run the following cmdlet:

Set-CASMailbox <User Identity> -EWSEnabled $TRUE 

NoteSome mailbox plans disable the EWS protocol explicitly. (For example, any kind of Kiosk plan does this.) Any manual changes that you make to an explicitly disabled feature will be disabled again when the mailbox plan is reapplied. Generally, this behavior occurs every 12 to 24 hours.

More Information

For more information about mailbox plans and about the features that are explicitly enabled or disabled by a given plan, click the following article number to view the article in the Microsoft Knowledge Base:

2987640 Your mailbox can't be accessed or has limited functionality after a mailbox plan is changed from Kiosk to another plan in Office 365 dedicated/ITAR

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