Microsoft Exchange 2003 18GB Limit

The bad news:
Exchange 2003 standard has a 18GB mailbox store limit..
The good news:
If you apply SP2 ,the mailbox store can be increased to 75GB(COOL),but the increase the mailbox is not automatically.You will need to tweak the registry to manually increase the limit from 18GB to 75GB.

To configure the database size for a database:
1. On the computer running Exchange Server, start Regedit.exe.
2. Open one of the following registry keys:
o To configure the database size limit on a mailbox store, open the following registry key: HKEY_LOCAL_MACHINE\System\CurrentControlSet
ServicesMSExchangeIS\Server name\Private-Mailbox Store GUID
o To configure the database size limit on a public store, open the following registry key: HKEY_LOCAL_MACHINE\System\CurrentControlSet
ServicesMSExchangeIS\Server name\Public-Public Store GUID

1. Right-click Public (or Private) Store GUID, point to New, and then click DWORD Value.
2. For the new value name, type Database Size Limit in Gb.
3. Double-click Database Size Limit in Gb. In Value data, type an appropriate value for maximum database size in GB. For Exchange Server 2003 Standard Edition, type a value between 1 and 75 (the default is 18 GB). For Exchange Server 2003 Enterprise Edition, type a value between 1 and 8000 (the default is 8000 GB). Click OK.
4. Right-click Public (or Private) Store GUID, point to New, and then click DWORD Value.
5. For the new value name, type Database Size Buffer in Percentage.
6. Double-click Database Size Buffer in Percentage. In Value data, type a value between 1 and 100 to specify when you want events to be logged to warn you that you are nearing the maximum size for a database. The default value of 10 will result in warning events to be logged when you have 10 percent capacity left before you reach the maximum size for that database. Click OK.
7. Right-click Public (or Private) Store GUID, point to New, and then click DWORD Value.
8. For the new name, type Database Size Check Start Time in Hours From Midnight.
9. Double-click Database Size Check Start Time in Hours From Midnight. In Value data, type a value between 0 and 23 to specify when you want Exchange to check the database size. The default value of 5 results in Exchange Server checking the database size 5 hours after midnight (5:00 AM). Click OK.
10. Close Registry Editor.