How important is mobile responsiveness in email design today?

You hear it everyday...mobile, mobile, mobile! To simply answer the question, you should always keep in mind how your email is going to look on a mobile device. Constant Contact makes it easy to see how your email would look on a mobile device when crafting your emails. This ensures your layout works for any customer on the go or anyone receiving your emails directly to their computers. 

How do you design your emails to ensure they are mobile responsive? Let me know below!