Many emails are viewed on mobile instead of desktop, designing for mobile is extremely important to get the highest clickthrough rates on content. This guide will have tips and tricks for designing for mobile. You can preview the mobile version easily and can also test send emails to see if directly on your phone.
Columns That Are Responsive vs. Not Responsive
To create columns that respond on mobile by dropping to a new row you can use the Responsive Column layout element. A Grouped Column will shrink the columns down to all fit on a single row.