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>
Are you still able to ping the box after this happens or does it become completely unresponsive? Any backups running during that time? Is this server a dedicated Exchange server or does it have other functions?

Otherwise, I agree witi Itai, you should cross reference the the event logs with the time in which your machine goes down. You may also need to get a dump of your system and post any pertinent information here. If it is just exchange that is failing and you still have access to your system, check Task Manager to gather what processes are running during that time.