The 'Preview' window in the system is designed so you can test out the functionality of your Links and Wild Cards while being able to see an example of how your message might look like upon delivery to the email client.
As all 'Email Clients' are coded differently they all have different rules on how they will format / display HTML email messages. This is why it is recommended to test test test!
To help with the testing process we have integrated an email testing feature into our accounts. (if you are in a tiered account structure and do not have this, please speak to your account administrator).