The System Attendant homeMDB attribute is missing or invalid

Applies to: Exchange Server 2010 EnterpriseExchange Server 2010 Standard


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

More Information

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