Wasn't really sure where to post this so sorry if it's in the wrong area, but we are intermittently losing Exchange access, it's a fairly simple setup just one Exchange server running 2k3R2 SP2, with Exchange 2k3 6.5.7638.1, everyone will just come in in the morning and not be able to access their email, via any method(OWA, OMA, and Outlook) when I go through event log on the server it's riddled with event ID's 3005 containing: Unexpected Exchange mailbox Server error: Server: [******] User: [***@***.com] HTTP status code: [503]. Verify that the Exchange mailbox Server is working correctly. I followed this article http://support.microsoft.com/?kbid=883380 and it seemed to solve the issue for two days and it is now back, when I restart the InfoStore, Exch Mgmt, MTA stacks, and Routing services it comes back up.

It appears your server has restarted.. check for any events related to event id 6000 + if it has not then AV or some other services have been blocking and stopping the services. You can find out when the server got stuck.

After increasing the max log size in order to see when the issue first starts, naturally there were so many 3005's that they would over write the beginning of the app log, I could see the logs immediately prior to the 3005's, and I found out that at 5am when Exchange checks the db sizes it was dismounting the primary first store db since it has reached it's 18GB cap for Exchange 2003SP2, followed this article to increase it to the maximum 75GB cap that is supports by exchange 2003 http://support.microsoft.com/kb/912375 Thank's for your help everyone!