What Does This Mean?
This means that people viewing email in Outlook may not be able to see your beautifully designed templates properly. Parts of these templates including, background images, bulleted lists and many positioning elements may not appear at all, or may be broken when viewed in these versions of Outlook.
What To Do About It
You can send plain text email to resolve this issue. You also have the option of sending HTML email, as long as you keep your formatting simple. As a rule, do not use any CSS elements (if you're not sure what those are, either ask your web designer or simply don't worry about it).
If you keep things simple, your Outlook users shouldn't notice anything out of the ordinary.
Alternately, you can simply accept that Outlook users may have trouble and provide them with a link to view your email as a web page. This allows you to use HTML email templates and other advanced styling features, while still allowing users of mail clients, that don't support those features, to have the option to see your messages as they were meant to be seen.