Quarantined messages are not stored in your actual account. They are stored on the systems providing the spam scanning service. Only released messages are stored in your account (INBOX).
If all the messages in your quarantine digest are spam, you can completely ignore the digest mail, and the quarantined messages will be automatically removed after 10 days.
You may also remove messages from your quarantine via the End User Web Interface. Once you've signed in, you can select the messages you wish to remove and click on Delete Message. You can also use the Delete All button to remove all the messages from the quarantine. Please be aware that once removed from the quarantine, messages are no longer available for retrieval.