SystemMailbox{guid} Mailbox: It holds schema information of any EXOLEDB (Store) event sink for the database Theres one System Mailbox for each mailbox databaseThe GUID in the mailbox name is the objectGUID of the associated databaseDirectory object exists in the MESO (Microsoft Exchange System Object) containerMailbox will be auto-recreated if its gone when mount the databaseIts not need to be removed for exchange decommission SMTP (servername-{guid}) Mailbox: Its a temp location for the messages in/out via MAPI, OWA, or MTA during categorization and advanced queuing in exchange 2003 Theres one SMTP Mailbox for each mailbox databaseThe GUID in the mailbox name is the objectGUID of the associated databaseDirectory object exists in the AD configuration partition [More info in the resource below]Mailbox will be auto-recreated if its gone when mount the databaseIts not need to be removed for exchange decommission Notes: SMTP Mailbox has gone in exchange 2007 and the later version System Attendant Mailbox: Its responsible for Free/Busy publish (OWA), move mailbox System Attendant mailbox is in the first mailbox database on each exchange serverDirectory object exists in the AD configuration partition [More info in the resource below]Mailbox will be auto-recreated on another database if the first database on the exchange server has been deletedIts not need to be removed for exchange decommission Notes: The Mailbox has gone in exchange 2010 Resources: Overview of Exchange 2000 Server and Exchange Server 2003 Special Mailboxes Breaking Change: The System Attendant mailbox has been removed from Exchange 2010MCITP | Exchange 2010/2007; MCTS