If the mailbox is corrupt when changing the quota, here are the steps to fix it.
Solution:
Login to your cPanel.
Select File Manager.
- Pilih 'Home Directory' dari File Manager Directory Selection popup.
Double-click on the Mail menu.
Double-click on your domain name (ie. Domain.com).
Double click on your email username (e.g. [email protected]).
Select the 'maildirsize' checkbox.
Select the Delete button from the top menu.
After you delete the "maildirsize" file, cPanel will refresh the disk usage of the email account automatically and this should fix the email quota size.