Log in to Directadmin. If you are not sure how to get here, you can look in this guide.
Then navigate to E-mail Manager -> E-mail Accounts
There you see all the email addresses you administer. You select the email address you want to delete and press Delete.
OBS! Keep in mind that all information will be lost on the account you want to delete. All emails, both sent and received, disappear
också.
Make sure Clean Forwarders is checked and then select DELETE