Event Type: Error Event Source: MSExchange Availability Event Category: Availability Service Event ID: 4011 Description: Process <ID>[w3wp.exe:/LM/W3SVC/1/ROOT/EWS-<ID>]: Configuration for forest <external domain name> was not found in Active Directory. Run the Add-AvailabilityAddressSpace command in the Exchange Management Shell for an Exchange Server 2003 Active Directory forest.
Note: This Event 4011 may cause confusing to the Exchange administrators because it is a normal situation that the Free/Busy data of external contacts is not available