Once an email is sent via FeedbackExpress, you'll be able to see them in the 'Sent Messages' section of your Amazon account. The messages won't always appear exactly as they will to the customer though, as Amazon's system strips out some features when displaying messages in the 'Sent Messages' section.
Stripped out features include images, formatting and links. This is why you may have a link 'View your order on Amazon' but this shows up on Amazon itself as just a line of text.
If you'd like to see the message the way the customer would, you can do this in FeedbackExpress by going to 'Campaigns' and clicking on the 'Sent' tab. Just click on the subject of any message to see it.