Starting in Exchange Server 2003 SP2, the database size for your Exchange Store can now reach 75 Gigabytes. By default, Exchange Server 2003 has a default database size of 16gigs, and when you reach that limit, Exchange will finish its transactions and dismount the store. If your default store size was 16gigs and you installed Exchange 2003 SP2 and wonder why you are having these types of problems, this is because Microsoft will only increase the default store size to 18gigs. As this might sound silly, it does make perfect sense. If Microsoft automatically increased the store size to 75 gigs, it would be easy to overlook what size your store is and you could use up all the space on your hard drive.
In order to configure your Mailbox store size you will need to edit the registry. As always, when working in the registry, please make a backup to ensure a quick recovery.
On the server running Microsoft Exchange 2003 SP2, click start -> run.
Navigate to HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\SERVERNAME\
You can modify the size of both the private and public mail stores. In this example we will modify the private store size.
Select the folder "Private-MailboxStoreGUID.
Right click on Private-MailboxStoreGUID and select New -> DWord Value.
Name the DWord Value "Database Size Limit in Gb" (without quotes).
Right click on Database Size Limit in Gb and click edit.
Choose decimal and change the value to the size you want to configure in GB.
EXAMPLE: If you have a 60gig system partition, you might want to configure you maximum size somewhere around the 40 to 45 gb so you don’t run into diskspace problems.
Select ok to save your settings.
Restart the information store service.
Upon restart, you should see Event ID 1216 under Application Logs which should reflect the changes you just made.
This information is provided "AS IS" with no warranties expressed or implied.