I have had this brought up by some co-workers and wondered if anyone from MS would like to officially comment? When Outlook 2003 was released there was the potential for un-patched Exchange 5.5 information stores to get corrupted or experience problems and dismount. Is Outlook 2007 officially (as in written somewhere - not just anecdotally) supported against a mailbox on an Exchange 2003 SP2 server? Comments welcomed.
Update: I finally found, buried here, this: Connectivity to Microsoft Exchange Server 2000 or later is required for certain advanced functionality in Outlook 2007.