Increasing Database Size Limit in Exchange Server Standard

The main difference between the Exchange Server Standard Edition and the Enterprise Edition is that it supports only 5 mailbox databases with a maximum database size of 1024 GB. If the size of your Exchange mailbox database exceeds 1TB, it will be automatically unmounted and user mailboxes in it will be unavailable.

In this case, the following event with EventID 40011 will appear in the Event Viewer:

Log Name: Application Source: MSExchangeIS Event ID: 40011 Task Category: MAPI Description: Exchange store MBX1: The logical size of this database (the logical size equals the physical size of the .edb file minus the logical free space) is 10302 GB. This database size has exceeded the size limit of 1024 GB, configured in registry key Database Size Limit in Gb at SYSTEM->CurrentControlSet->Services->MSExchangeIS->EXC2->Private-database GUID.

The fact is that the maximum database size in Exchange Standard is strictly limited to 1024 GB. However, you can increase this limit

To do this, you need to get the mailbox database GUID:
```
Get-MailboxDatabase -Identity MBX1| Ft Name, GUID
```
Then open the Registry Editor (regedit.exe) and go to the registry key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\<YourServerName>\Private-<your-db-GUID>;
Specify the maximum database size you want to set in the Database Size Limit in GB registry parameter. If this parameter is missing, create it manually (DWORD type);
Restart the service and Microsoft Exchange Information Store (MSExchangeIS) using PowerShell or services.msc:
```
get-service MSExchangeIS| restart-service
```
Mount the database with the –Force option:
```
 Mount-Database -Identity MBX1 -force
```

Notes.

If your database is in a DAG, you need to apply the registry change on all Exchange servers with a mailbox database copy;
Automatic switching won’t work when using DAG. To activate a copy of the database on another server, you need to switch it manually and mount it with the -Force attribute;
Changes in the registry will be removed after installing the next Cumulative Update (CU).

This article applies to Exchange Server Standard 2019/2016/2013/2010.