No email accounts have been created on the domain but still the mail folder is taking up huge space.
When a cPanel account is created, a default email account with the cPanel username is also created automatically.
In this case it seems that it has been set as catchall which is why any email sent to the domain at [email protected] is saved under the default email address. You can delete them via Webmail .
(cPanel >> Email Accounts >> At the bottom, you will see the cPanel username and a Webmail icon besides it. Login to it using your cPanel password and delete the emails.)
To disable catchall and prevent this from happening again, do the following :
1. Login to the cPanel of the domain.
2. Click on ‘Mail’ icon.
3. Click on ‘Default Address’.
4. Click on ‘Set Default Address’ link.
5. Enter :fail: in the text box and click on ‘Change’ button.
This should fix the problem!