In the Web-based Administration, the user mailbox size quotas are set on the Users page. Click on the targeted User in the list on the page and the User Edit page will open.
Select the Quota Status in the list box and then enter the values of the Disk and Grace Quotas. Click the Save Changes button to accept and apply the changes.
From the Control Panel Applet, select the Users tab. Double or right-click on the targeted user (and select Edit if right-clicking). The Edit User dialog box will open.
Control Panel Applet Edit User dialog box
Scroll down in the users options list box and select the User Mailbox Quota check box and then click the Details button at the bottom of the dialog box. The Mailbox Quotas dialog box will open.
Note: The check box must be filled in order to "enable" the quota.
Control Panel Applet Mailbox Quotas dialog box
Select the Quota State in the list box and then enter the Disk and Grace Quotas in the text boxes provided. Click OK to accept the changes to the quotas and then click the Apply button on the Control Panel Applet to apply the change for the user.