ErrorMailboxStoreUnavailable when sending requests from Outlook Rest API RRS feed

  • Question

  • Hi,

    We are developing a web application that uses the Outlook Rest API to perform all email operations (getting/sending/moving messages and so on). For a few of our clients we constantly(but not for every request) get this error:
      503: {"error":{"code":"ErrorMailboxStoreUnavailable","message":"The mailbox database is temporarily unavailable."}} 

    They have reported that they started having issues also with their original email client for sending messages for example. Why can that be? In our application, we have followed all good practices for batch requests.

    Thanks for the response in advance!


    Wednesday, January 10, 2018 9:07 AM


  • The error means the Mailbox is temporally unavailable the most common cause of this in Office365 is that the Mailbox is being moved from one server to another due to maintenance of servers (eg applying patches, updates and other server related issues). Usually you can tell this by looking at the headers which tells which backend server processed the request. If you being throttled you should receive different error messages (usually with a backoff or retry internal suggestion) a place to start would be look at the full response that is being returned in something like fiddler.


    Thursday, January 11, 2018 5:02 AM