We have IIS hosting OWA that is the web frontend to 3 backend exchange servers. Yesterday we got a lot of event 9791 warnings: "Cleanup of the DeliveredTo table for database 'Second Storage Group\Mailbox Store EUROPE 2' was pre-empted because the database engine's version store was growing too large. 0 entries were purged. At this point the server was crawling. Our Mail admin is currently away and not contactable so we rebooted the server. Everything seems ok when reading mail from outlook and evolution-mapi clients but OWA and active-sync connections cannot access. When logging into OWA, users whos mailboxes are not on this backend server are fine but users on this server can log into the OWA frontend but once submitting their credentials the page returns a 503 service unavailable error. We have since rebstarted the affected exchange server and the IIS server as well as iisreset /noforce but problem persists. Can anyone suggest what we should look at...