Login to your club control panel.
Click the Settings tab, then select Email address from the left-hand menu.
Under the Mailboxes section, you should find a list of created mailboxes that are associated with your club’s custom domain name.
Towards the right of each listed mailbox, click Delete.
After clicking the delete button, you will be asked if you are sure if you want to delete the email inbox. Once the mailbox is deleted, it cannot be recovered.