To view all messages that were held by the spam filters, first navigate over to the spam section. You can click on the 'Spam' button at the top of the page after you log in.
When you reach the spam page, navigate over to the right side of the page. In that section, you'll be able to choose your view. To view Held messages, click on the link that says "Held Messages".
You can see a short preview of the message content by clicking on the subject line of the message. It shows the first segment of the list message, unstyled. To view the full message or any attachments, you should release the message.