I created an outbound Content Filter which adds the header 'X-Ironport-Quarantine'. I tested by sending an email outbound, which was caught by the Content Filter and sent to the ISQ. I click on the URL received through Spam Notifications for self service, but I can only see inbound mails held in the ISQ. If I go in as admin, I can see the email held in the ISQ. Is this correct, or should I be able to release outbound through self service?
I assume the test message was send to an external address, so that recipient would get the notification and then can access/release the message. So that's why you do not have it in your list, as the sender usually does not get notified. That's one thing to consider when you configure outbound spam scanning, in general it's not useful to enable spam notification for this, as the recipient is an external address that does not have access to the quarantine.