I'm not sure how long this issue has been happening, but recently a few of the remote sales users were going to a sales meeting and wanted to set their Out of Office... however in Outlook 2010, they get this error message: "Your automatic reply settings cannot be displayed because the server is currently unavailable"

When I run the Exchange Remote Connectivity Analyzer, Autodiscover completes fine, but the next step fails:

Exception details:

Message: The request failed. The remote server returned an error: (403) Forbidden.

Type: Microsoft.Exchange.WebServices.Data.ServiceRequestException

Stack trace:
at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.GetEwsHttpWebResponse(IEwsHttpWebRequest request)
at Microsoft.Exchange.WebServices.Data.MultiResponseServiceRequest`1.Execute()
at Microsoft.Exchange.WebServices.Data.ExchangeService.BindToFolder[TFolder](FolderId folderId, PropertySet propertySet)
at Microsoft.Exchange.Tools.ExRca.Tests.EnsureEmptyFolderTest.PerformTestReally()
Exception details:
Message: The remote server returned an error: (403) Forbidden.
Type: System.Net.WebException
Stack trace:
at System.Net.HttpWebRequest.GetResponse()
at Microsoft.Exchange.WebServices.Data.EwsHttpWebRequest.Microsoft.Exchange.WebServices.Data.IEwsHttpWebRequest.GetResponse()
at Microsoft.Exchange.WebServices.Data.ServiceRequestBase.GetEwsHttpWebResponse(IEwsHttpWebRequest request)

I've done some research, but I have yet to find a working fix for this... it seems like some permissions are messed up in IIS, but I haven't figured out what.