[EWS] [Exchange-Online] Http error 500 CAS server not available RRS feed

  • Question

  • We have a customer using our software to connect to via EWS. The application creates messages in the user's mailbox. We are seeing intermittent http error 500, with the fault string "Exchange Web Services are not currently available for this request because none of the Client Access Servers in the destination site could process the request.".  The software then retries the request, and usually succeeds.  I have not seen this error with other customers, just this one.  Why does that happen, and what can be done about it?

    Saturday, October 11, 2014 6:09 PM


All replies

  • You need to make sure you add the X-AnchorMailbox header to each of your requests and ensure it's set to Mailbox your trying to access see


    Monday, October 13, 2014 4:12 AM
  • Hi,

    As per the information and details provided by you, I think you should: -

    • Check the Require SSL check box under Exchange Web Services (EWS). Often, this is done under Autodiscover instead of EWS.

    • Perform  a reset of the Synchronize Connection and Excahnge Mailboxes (SIB) from the Edit Unified Messaging Account page.

    I hope this information will be helpful for you.

    Thanks and regards



    Monday, October 13, 2014 10:15 AM