Once upon a time, you could launch mass email campaigns with the assumption that a significant portion of the emails would find their way to a desktop computer. But no longer.

Smartphones have changed the game. To better understand the challenges you now face, let’s carefully consider the perspective of the smartphone user.

Enter Pete, your typical smartphone user. Pete is a thirty-something male who purchased an iPhone last October. He uses it frequently to change his Facebook status, upload vacation pictures, tweet witty opinions, check the weather, browse YouTube videos, text his friends, and check his email—all while he drops off dry cleaning, picks up a latte, walks to the office, and eats a burrito for lunch.

As you can see, your message in Pete’s inbox has a lot of competitors for his undivided attention. In fact, there are so many competitors that nothing wins Pete’s sustained attention for long, and you have to be smart to get a slice of it. This is the new game.

Here is what you need to know to play it well.

#1: Pete Will Read Your Pre-Header

When Pete receives your message on his smartphone, he is going to see three things, one right after the other. The first is the sender (you), the second is the subject line, and the third is the preheader (the first few lines of your email). If you don’t make the most of it, the preheader may be all that Pete reads of your email before deleting it.

Your goal is to get Pete to open the email based on what he reads in the pre-header. Come up with something catchy, or link a plain-text version of the email in the preheader (remember that not all mobile devices can read HTML). The preheader does not have to be fancy, but it should be inviting.

#2: Your Email Is Under Pete’s Thumb

After Pete has read the preheader and then opened your email, he is open to encountering any number of frustrations. Maybe that important cheeseburger image didn’t load. Or maybe your double columned newsletter is difficult to navigate now that it has been shrunk to microscopic proportions. Or maybe you stacked three links right next to each other and his giant thumb can’t open the middle one.

You do not want Pete to face any of these problems. The best way to avoid them is to check what your email will look like on a variety of mobile devices. There are websites that will provide demo versions for different mobile devices. Find one and test your design before you send out a mass email. In short, your email should be understandable, readable, and clickable no matter what screen Pete uses to read it