You can use this guide to delete a mailbox using the Client Management Portal.
First go to Products & Services (you must be logged in to use this link) and pick the appropriate hosting package.
Delete a Mailbox
Warning: Deleting a mailbox will permenantly delete its contents from our servers. This cannot be undone.
- Click on Mailboxes in the sidebar

- Click the bin icon next to the mailbox in question

- Click Delete Mailbox
