Outlook clients may be unable to set OOF status or view Free busy in an Exchange Server 2013 coexistence environment

Original KB number:   2956962


In a Microsoft Exchange Server 2010 and Exchange Server 2013 coexistence environment, Outlook clients may be unable to set out of office or view free or busy information. Specifically, clients may experience the following symptoms:

  • When you try to schedule meetings, the free or busy times for attendees aren't displayed. Only hash marks are displayed for attendees.

  • When you try to set the out of office, attendees may receive the following error message:

    Your Out of Office settings cannot be displayed, because the server is currently unavailable. Try again later.

Additionally, the HTTP proxy will display the following HTTP exception for each failed proxy request:

Cannot find the appropriate SOAP header or body.


The Internet Information Services (IIS) uploadReadAheadSize attribute configures a limit for the number of bytes in the entity body of a request and the number of bytes that a web server will read into a buffer and pass to an ISAPI extension. This issue occurs because the setting for the uploadReadAheadSize attribute is too small.


To resolve this issue, increase the size of the IIS UploadReadAheadSize setting on the Exchange Server 2013 CAS role. To do this, follow these steps:

  1. Open IIS Manager.

  2. Expand Sites, expand Default Web Site, click the EWS virtual directory, and then click Configuration Editor on the feature page.

    Screenshot for selecting Configuration Editor.

  3. In the Section box, expand system.webServer, and then click serverRuntime.

    Screenshot for selecting the serverRuntime node.

  4. Set UploadReadAheadSize to 49152.

    Screenshot for setting the UploadReadAheadSize value.

  5. Run the iisreset command to reset IIS.