Not getting the results you’d hoped for from your latest email campaign? The reason could be that your emails aren’t mobile friendly.

According to mobile research by the Pew Internet Project, 52% of adult American smartphone owners use them to send and receive emails. That’s potentially half of the audience for your communications.

Have you taken a look lately at the emails you’re sending, from a smartphone user’s perspective?

Is copy displayed in a single, easy-to-read column? This column should be at most 600 pixels wide and the font size should be at least 13. If you use a responsive email design, this is taken care of automatically.

If you’re not up on responsive design, it’s basically digital design that adapts gracefully to whatever screen it finds itself playing on. If you’re the hands-on type, you can learn more about it here. If not, consider upgrading your email template to one that’s responsive (here’s a list of free and inexpensive ones).

Next, consider the amount of copy in your messages. Shorter is usually better, but longer is okay – if there’s a very good reason for the copy to be there. If not, the delete key is your friend. And think twice about using a big word if a little one will do. As always, simplicity is sophisticated.

Now look at your images. Do they tell a story that complements your text? Do they load quickly? If not, swap them for ones that do – or modify them in your favorite image editing software to get the file sizes down. Keep in mind that although many email apps display images by default, some users turn automatic image viewing off, so make sure your copy can stand on its own if it has to.

Look at your call(s) to action next. Ideally, you’ve got more than one. And they should be very clickable/tappable. They should stand out visually from the rest of the email, without being garish and/or annoying (flashing, bouncing buttons may get attention, but it’s probably not the kind you want).

Another note about CTAs: there should be no doubt about what you’d like the reader to do – and what they’ll get from doing it. Tough to do in a word or two or three, but essential.

Finally, look at the email as a whole, from your customers’ perspective. Is the purpose of the message immediately clear, without scrolling? Does the overall look and feel reflect your brand in a simple, straightforward way? What does it look like without images – does it still achieve your goal for sending it?

Mobile is big and it’s only going to get bigger. Getting customers to open and respond to your messages is tough enough as it is – don’t make it tougher on yourself (or them) with emails that aren’t mobile friendly.