When you configure a federation trust between a local Microsoft Exchange Server organization and a remote Exchange Server organization, users from cannot see the free/busy information of the users in the remote organization.
Additionally, the following errors are logged in the event log on the local Exchange server:
Event Source: MSExchange Availability Event ID: 4001 Description: Process Microsoft.Exchange.InfoWorker.Common.Delayed`1[System.String]: <>SMTP:firstname.lastname@example.org failed. Exception returned is Microsoft.Exchange.InfoWorker.Common.Availability.AutoDiscoverFailedException: Autodiscover failed for e-mail address <>SMTP:email@example.com with exception System.Web.Services.Protocols.SoapHeaderException: An error occurred when verifying security for the message.
Event Source: MSExchange Availability Event ID: 4002 Description: ProxyWebRequest FederatedCrossForest from S-1-5-21-3124261755-470644396-3029476549-1139 to https://autodiscover.domain.com/ews/exchange.asmx failed. Caller SIDs: WSSecurity. The exception returned is Microsoft.Exchange.InfoWorker.Common.Availability.ProxyWebRequestProcessingException: System.Web.Services.Protocols.SoapHeaderException: An error occurred when verifying security for the message.
Also, HTTP 500 responses returned for Availability requests on the remote forest Exchange server are logged as follows in the W3SVC logs:
This issue occurs because the WSSecurity property of the "EWS" virtual directory or the "Autodiscover" virtual directory is disabled on the Client Access servers in the local Exchange Server 2010 organization.
Exchange 2016 or Exchange 2013 To resolve this issue, reset the WSSecurity authentication for the virtual directories on the Exchange Back End site for each server in the remote organization.
Open Windows Powershell and add the Exchange Management snap-in.
Microsoft Exchange Server 2010 Enterprise, Microsoft Exchange Server 2010 Standard, Exchange Server 2016 Enterprise Edition, Exchange Server 2016 Standard Edition, Microsoft Exchange Server 2013 Enterprise, Microsoft Exchange Server 2013 Standard