You can deactivate your account at any time. However, before doing so, you must first deactivate all active mail subscriptions.
To deactivate or delete your account, go to the 'Manage account' tab under Settings then click on 'Deactivate account'. Your account will automatically be deleted after a period of one year in which no mail is received. Should you still receive mail despite deactivating your mail subscriptions, you will be notified as usual by mail. Your account will be permanently deleted after a period of one year in which no mail is received.