Question: My Exchange Server 2003 (running on Windows Server 2003) fails at around 04:54 on a regular basis, though not necessarily every day.

By "fails" I mean that my colleagues try and check their emails and Outlook says "outlook is not connected to exchange." Since outlook tries to update the email every 3 minutes or so, and it records the time when the folder was last updated, it is possible to see the time of failure.

It is impossible to download emails until the server is restarted. Thereupon everything works well.

I have looked in Scheduled Tasks and can't see anything pertinent.

Does anyone have any ideas?

Answer: 
**Question:**

a) What version of exchange 2003 are you using ? Standard or Enterprise 

b) Is this part of SBS2003 or a stand alone exchange.

**Suggestions:**

1) Can you navigate to this path in registry.

HKEY\_LOCAL\_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\Server name\Private-Mailbox Store GUID

Check if you have a key called 
*Database Size Limit in Gb*
and what's the value there.

2) Whats the DB size on disk?
Default priv1.edb path is c:\Program Files\Exchsrvr\MDBDATA

**Possible Causes:**

a) Exchange 2003 DB is dismounting because of 18GB hard limit for Exchange 2003 standard.
This is usually resolved by increasing the db size limit to 75GB for Ex03 Standard. 

ref:
<http://support.microsoft.com/kb/912375>

White-Space / Offline Defrag's etc, to reclaim space:
<http://www.msexchange.org/tutorials/exchange-isinteg-eseutil.html>
Yeah, SP2 might do it. If you still have issues, Google for "exchange 2003 sp2 hotfix" and see if any of them are relevant to your problem. Another workaround is to set the Exchange Information Store to automatically restart after a failure in services.msc (if that's the service that's failing), but this doesn't fix the root cause of the problem.