While marketers have been using email for decades, the biggest impact on this platform has come in the last three to five years due to the quick and exponential increase in smartphone adoption, thus leading to a change in how emails are viewed.

Mobile email is the one thing that most blurs the line between personal and public, as people are moving in droves to have both personal and work emails on the same phone. The reason? In this day and age, they always have their phones with them.

People have an emotional attachment to their smartphones, a relationship that does not exist with other devices. This attachment is so strong that, while a broken computer, stove or even car—all products used on a daily basis—may take a couple of days to get repaired, a lost or broken phone will typically get replaced the same day. Also, while a user will generally forget a negative experience on a desktop computer, the same experience on a mobile phone produces a much stronger reaction and implication.

The answer to both of these guidelines is responsive design, a Web development approach that has a mobile-first philosophy to providing optimal viewing experiences.

The big advantage of responsive design for mobile is that emails are rendered specifically to the individual device that is opening the email, while only maintaining one single code base on the back end. This approach will not make an email perfect for every device, but it will scale elegantly across multiple devices to allow for the best customer experience, however the content is viewed.

Responsive design works by using a CSS technique to determine where the email is being opened and then renders appropriately to fit the device’s screen size. A helpful tool in verifying how an email will look across multiple devices is an open source program called Responsivator, developed by John Polacek, a senior engineer at Draftfcb.