things like car rental confirmations and airline reservations are marked negatively because they 

• Plan Text or Html message is base 64 encoded  (60)
• Body contains unnecessary character encoding (30)
• Email contains a web bug= ... allowing the sending to validate recipients email address (60)valot
• Bayesian Analysis suggests there is a 98% chance this message is junk (68)

other emails like for airline miles people sign up for are getting marked negatively for having works like EARN in them.

how do we make this less likely to mark these legit messages from companies so negatively?