Hi Andrea,
A Sales Email is a Marketo hosted email sent specially from a sales person either through Sales Insight in salesforce or the outlook plugin. You would need to enable these Marketo emails for sales to send them. Here's an article on how to do it: http://community.marketo.com/MarketoArticle?id=kA050000000L9imCAC.
An email sent through SFDC will not be tracked.
Hope this helps.