Today I found my CPanel displays wrong disk quota for an email account. It shows 58/100 MB (58 MB used, of 100 MB preserved) while actually the mailbox is empty.

I have checked with du -sh command (a command to check disk usage) and it returned 100 KB or something, so there must be something wrong.

After googling around, I got some trick to solve this problem. Perform this action from shell/SSH or simply using file manager in CPanel:

1. Go to /home/usercpanel/mail/domain.com/emailaccount/.
2. Delete file named maildirsize, this file stores disk usage information
3. Change the number of disk quota for that email account from CPanel (inside menu Email Accounts), it will regenerate a new maildirsize file.

Refresh your browser and now you should see the correct disk quota for that email account.