If you want to apply mailbox quotas to all mailboxes, this should be set on each mailbox database on your Exchange server.
In Exchange Management Console, expand Organization Configuration > Mailbox. Right click on the DB and select properties. Changes can be made on the Limits tab.
If you need to make an exception to the default quotas for a mailbox, this is done in Exchange Management Console.
Expand Recipient Configuration > Mailbox. Open properties of the mailbox you wish to edit the quotas for. On the Mailbox Settings tab, select Storage Quotas > Properies.
Untick ‘Use mailbox database defaults’. Modify as required.
By default, any changes made to quotas will take up to 2 hours to take effect. We can make registry changes on the Exchange Server to reduce the interval.
Load regedit (running as a user with Exchange Server Admin rights and Admin rights on the server).
Go to HKLM\SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem
Create a new DWORD value “Reread Logon Quotas Interval” (without the quotes) and give it a decimal value of 200. (That’s 20 minutes in seconds)
Still under the key ParametersSystem create a new DWORD value “Mailbox Cache Age Limit” and give it a decimal value of 20. It makes sense to keep this age limit the same as the refresh interval..
Restart the Exchange IS service.