Global Settings: You can configure mailbox quotas from the Exchange admin center (EAC) web interface. To do this, go to the section Servers > Databases > select the required database > Properties > Limits. Set the necessary quotas on the Limits tab.
Customize Per Mailbox: Mailbox quota settings can also be changed from EAC (Recipients > Mailboxes > Properties > Mailbox usage > More Options > Customize the quota settings for this mailbox).
Example: Change to “unlimited” instead of 2GB default maximum.
Issue a warning at (GB) 9.9
Prohibit Send at (GB) “unlimited”
Prohibit send and receive at (GB) “unlimited”