Even though it is definitely always a better idea to migrate or transition from one version of Exchange to another version, by deploying the new version next to the old one, and moving all mailboxes, public folders, and other functionality before decommissioning the old Exchange server, it may not be possible in some situations. But, you cannot always turn to in-place ugrades, as can be seen in the following overview.
In-Place Upgrade:
- From Exchange 5.5 to Exchange 2000 = Supported
- From Exchange 5.5 to Exchange 2003 = Not Supported
- From Exchange 5.5 to Exchange 2007 = Not Supported
- From Exchange 5.5 to Exchange 2010(beta) = Not Supported
- From Exchange 2000 to Exchange 2003 = Supported
- From Exchange 2000 to Exchange 2007 = Not Supported
- From Exchange 2000 to Exchange 2010(beta) = Not Supported
- From Exchange 2003 to Exchange 2007 = Not Supported
- From Exchange 2003 to Exchange 2010(beta) = Not Supported
- From Exchange 2007 to Exchange 2010(beta) = Not Supported