The "view source" method in Outlook 2010 shows you only the HTML code of the body of the email. It does NOT show you the actual source code of the email itself, which is considerably more complex, and may include a text-only version of the body as well. Sometimes it is necessary to look at the actual code of the email, in the form it arrived in, in order to troubleshoot a display oddity, etc.
If I recall correctly, in order to have the email's body code appear along with the header when you click Properties, you'll need to meddle with the registry. The Registry solution given above might or might not be correct. It did NOT work for me. The solution was to drill down in the registry a bit further, as instructed here: http://email.about.com/od/outlooktips/qt/How_to_View_the_Complete_Message_Source_in_Outlook.htm
Remember to restart Outlook 2010 after exiting the Registry. The true email source code will appear under the header code in the "Internet headers" portion of the popup you get with File>Properties. Outlook will show you the full body source ONLY for emails received AFTER you've made the proper Registry edit. For emails received prior to that, you can see their HTML source code using the Actions menu, but their email source code cannot be retrieved. The file size displayed in your list of emails will be a larger number of bytes than would be displayed before making this change. (Something I discovered only because I happened to be getting duplicate emails from my mail provider. Maybe some were received before my change, some after. Time will tell ...)
Viewing the source of just created mail isn't possible? – ThiloL – 2012-04-12T09:06:40.823