When you set up merge fields in an email, the merge tag is looking at the associated list data for that contact, and inserting that information into the body of your email. When you test your email, you are simply adding an email address into a form. Even if the address is included in one of your contact lists, the form on the preview page and your mailing list don't connect, and your merge field won't work.
If you need to test your merge fields, first set up a small list for testing, and then select that list on the preview page for your email campaign. Check out the step-by-step guide below to set up your list and send a test email.
1) Create a new mailing list for testing. (Do this by clicking on Lists, and then New.) Include yourself and any coworkers or friends that you want to test your email with you. Make sure to keep it under 10 contacts, or it won't appear on the preview page.
2) In the Preview page of your email, select the "Mailing List" option.
3) Any mailing lists that have less than ten people will be displayed; choose the one that you have designated as your test list.
4) Press "Send Test Email"
5) Your test e-mail will now include active merge-fields.