You must run Setup again if you want to add or remove components (such as connectors) after you have already installed Microsoft Exchange Server. You must also run Setup again if you want to upgrade to a later version of Microsoft Exchange Server or if you need to restore the registry because it has been corrupted. When you rerun Setup, it detects the existing Microsoft Exchange Server installation on the computer and starts a maintenance installation. Maintenance installation includes the options Add/Remove, Remove All, and Reinstall. If you are upgrading from a previous version of Microsoft Exchange Server to version 5.5 or are installing a service pack (SP) on a version 5.5 server, maintenance installation includes an Upgrade option instead of a Reinstall option.