ReportMail offers a free built in spam assassim check but if you opt to use the Inbox preview tool an advanced spam check is also included.  

This provides a detailed breakdown of your content and the email code against key spam filters. By showing you all the words that are acquiring spam weightings in the email, it is much easier to write the copy and change any flagged elements before the send.

A simple check can make the difference between getting into the inbox and making the campaign a success.