You can review your e-mail accounts currently in use, as well as their disk space usage. This will help you to determine whose accounts need to be cleaned up, or allow you to manage disk space, or delete unused accounts.
Login to WebMail as your e-mail admin account, [email protected].
Click on Settings.
Click on Email Account Management
Here you can see all your accounts and their disk space usage.
You should make sure to DELETE any accounts not in use, by checking the box, to the left, then clicking the Terminate button at the bottom of the page.
Otherwise, you can then log in to the account and delete or clean up e-mail messages to reduce the disk space usage. If this account belongs to one of your users and you are unsure on what to delete, notify your user that they need to clean up their e-mail account.
Repeat these steps as needed.