How to manage customer with two email addresses

I have students with two email addresses. Their main one fro normal communications that they annotate on their online application. Then when they order a course(s) - we are an online seminary - they may use another one just for their orders. What happens then it that I have two contact records for the same person. Is there a way to somehow mesh the two email address to just one record for that student? In other words, when they make an order, it goes to the one mail record with their preferred email address.

Does the 2nd email address in their record solve this issue? Thank you. Gary