Some or all of the following may be seen in a Microsoft Exchange 2010 Server environment:
The System Attendant mailbox appears under Disconnected Mailboxes in the Exchange Management Console (EMC)
Users are unable to retrieve the free/busy information for Exchange users Event ID 8197
Search Indexing fails with a MapiExceptionUnknownUser error
Move Mailbox fails with: "hr=0x80040111" "ec=1010"
When you perform MAPI connectivity tests by running a cmdlet, such as the test-mapiconnectivity -verbose cmdlet, you receive a Microsoft.Mapi.MapiExceptionUnknownUser result
The System AttendanthomeMDB value is missing or invalid.
To address this issue, use the ADSI Edit tool to determine the distinguished name of the appropriate mailbox database, and then set the System Attendant homeMDB attribute accordingly. The specific instructions can be
For more information on this topic, including a step by step resolution, see the following document from Microsoft TechNet online:
The System Attendant homeMDB attribute is missing