For several reasons I had MS Exchange get into a state on a customers Windows 2003 SBS Server today, that required a re-install of Exchange over the top. I think this was mainly to correct IIS issues and related stuff.I did also need to backup and restore the information store since after the 'disasterrecovery' setup the correct information store data could not be seen by certain (Exchange) services.

Anway, the command to use is "setup /disasterrecovery" (or for SP2, "update /disasterrecovery"). And I also had to re-register the pop connector / vitrual server with IIS using  " \Program Files\Microsoft Windows Small BusinessServer\Networking\POP3\imbreg.exe" Otherwise the sender of any email INWARDS gets an NDR. This is possibly only applicable if you use POP3 to get the email off the Exchange server.