Exchange Server 2007 “Service Unavailable” on /public

This appears to be caused by the Public Folders database not mounting correctly, despite the Exchange System Manager saying it has. This is usually due to replications being missing from some of the system public folders. Dismount and them re-mount your public folder database, then go in to Event Viewer and look at the application log. This will probably show you errors, the detail of which tells you the replication(s) that is(are) missing. Fix those, leave them to replicate, then try dismounting and remounting your public folder database again. You should get a clean mount in the Event Viewer.

Once it works, should produce a login box, and not just a “Service Unavailable” error.