Mastering email marketing is as much about sales instinct as it is raw data.  Data is such a useful tool when trying to make vital decisions about just what should go into your email.  This awesome piece from Direct Marketing tells us that six to 10 word long email subjects are one of the keys to success, but there are plenty of others inside.

http://www.dmnews.com/email-marketing/how-to-send-the-almost-perfect-email/article/449482/