Using multiple databases to store mailboxes allows you to configure a different volume.
Example: The DBMX01 database stores mailboxes with a 1GO quota and the DBMX02 database stores mailboxes with a 5GB quota. With this configuration, simply move the box from one base to another to change the volume.
Add a database
5. Restart the Microsoft Exchange Information Store service with the following PowerShell command:
The management of the volumetry is explained here.