exchange on sbs 2003 mailbox store limits?

(Service Pack 2) To expand the Exchange database, or set a limit between 1 & 75GB:

Open regedit and navigate to HKLM\SYSTEM\CurrentControlSet\Services\MSExchangeIS\SERVER_NAME\Private-STORE_GUID. To change the Public store limit, navigate to HKLM\SYSTEM\CurrentControlSet\Services\MSExchangeIS\SERVER_NAME\Public-STORE_GUID.
In the event your Exchange server has more than one private or public store the GUID of each store can be found by running ADSIEDIT.msc and navigating to:

CN=MAILBOX_STORE_NAME (SERVER_NAME),CN=STORAGE_GROUP_NAME,CN=InformationStore,CN=SERVER_NAME,CN=Servers,CN=First Administrative Group,CN=Administrative Groups,CN=Organization name,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=domain,DC=com

SERVER_NAME, STORAGE_GROUP_NAME, and MAILBOX_STORE_NAME reflect the mail store to be changed. Then take note of the objectGUID:… value for that mail store.

Create a new REG_DWORD value in the registry key for the correct GUID. Name it “Database Size Limit in Gb” and set the value from 1 to 75.
Assuming you are newly setting the “Database Size Limit in Gb” value, it will be detected at the next size check. Reboot the Information Store service for immediate recognition.
By setting the “Database Size Limit in Gb” key the mailbox store will not exceed that value. When the mail store reaches 90% off that value, a default 10% buffer is allowed, it will begin to log event ID #9689 to notify you that the store limit has been reached. Once the mail store does reach the maximum limit the first size check, which happens every 24 hours at 5am, will not take the database offline. The second size check will dismount the store that exceeds the limit.

Both the % of the mail store used as a buffer and the time of the database size check can be changed within the same GUID registry key referenced above. To set either, create a REG_DWORD value named “Database Size Buffer in Percentage” or “Database Size Check Start Time in Hours From Midnight”. Set their values from 1 to 100 or 0 to 23 to change, respectively, the buffer % or the offset from midnight for the size check.

The Exchange 2003 Enterprise information store can also be limitted by the “Database Size Limit in Gb” key. The valid range of values is 1 to 8000. If the key is not set, the default value is 8000GB.

It still amazes me that the Exchange System Manager doesn’t have settings for either “max. database size” or “min. disk space remaining on server”. Isn’t that the whole point of Exchange? …that it’s faster and easier to run because it doesn’t require the amount of experience and forethought that Postfix does.

Ref: http://www.mrtweak.com/exchange-server/registry-tweak-to-set-a-75gb-store-limit-on-exchange-2003-standard-sp2/