If you experience this error message "Invalid Maildirsize File" when attempting to try and change the email account quota in your cPanel we have a solution that will fix it.
Here is the manual how to get rid of the Invalid Maildirsize File error in cPanel server:
1. First login to your cPanel web hosting account via ftp with the username and password
2. Go straight to the "mail" folder. You will see it when you login to ftp. The full path on cPanel web hosting server should be: ../mail/domain.com/[email protected] (domain.com is your actual domain name you are using with the hosting account)
3. Then from this folder you can delete the hosting file with name: "maildirsize"
4. Once this cPanel maildirsize file is deleted from your web hosting, login to your cPanel and change the mail quotas. This will automatically re-create the maildirsize file correctly by cPanel.
You should be now able to change quotas for all email account(s) in your web hosting.