To view a message as it will appear after you send it, you want to Preview the message.

If you are in the process of creating a message, and are in the message creation screen, simply click Save Changes and Preview.

If the message was already created and you want to go back and see a Preview of it, go to Messages and click Manage Messages.
Choose the message you would like to preview.
In the Action column on the left, click the link to Preview.

Your message will open in a new window and you will be able to see the final version of the message. If you used any Personalization Tags, they will continue to appear as code in the Previewed message. They do not resolve and populate with the presonalized data until the email is actually sent. You must send yourself a test message to ensure that the personalization tags are resolving/populating correctly.