Did you know that 38 percent of emails are now opened on mobile devices? In fact, when you look at the numbers, mobile devices are No. 1 in terms of opens.

Despite this fact, more than 50 percent of marketers are not designing emails for mobile devices. This is a huge oversight that could affect the overall effectiveness of an email marketing campaign, especially when it comes to newsletters.

If you don’t optimize your email newsletters for mobile devices, you’re potentially limiting the number of people that act on your email messaging.

Thankfully email newsletter optimization for smartphones and other mobile devices is not difficult. Here are the most important best practices.

• Keep Subject Lines Short: Email subject lines on mobile devices get shortened because of the limited screen space. As a rule of thumb, try to keep your subject lines under 40 characters. That’s about five to six words. As an example, the subject line “Carbon Monoxide: Is Your Home at Risk?” is 38 characters.

• Shorten the Width of Your Emails: The magic number seems to be around 600 pixels for the width of an email newsletter. To give you an idea, the width of an iPhone screen is 480 pixels. Six-hundred pixels makes emails appear viewable on smartphones while at the same time not making them seem too narrow on computers as well as tablet devices with larger screens such as the iPad.

• Make It Touch Friendly: For important links that take people to articles and other important content, consider using buttons as opposed to hypertext links. This makes it easier for people with fat fingers to click on links with a smartphone.

• Consider One to Two Columns: When you go past two columns in an email newsletter, it starts to get very difficult to view without a lot of pinch-zooming on a smartphone. Try to keep your newsletters to one or two columns to make it easily viewable on smartphones.

• Have a Mobile Blog and Website: You should have a mobile friendly version of your website and blog. It makes it easy for people on mobile devices to view newsletter content that’s on your website or blog. Mobile web pages should not contain any Flash. JavaScript, HTML5 and CSS3 are compatible alternatives for mobile devices.

• Start Using a Larger Font Size: Typically marketers use a font size anywhere from 10 to 12 points for body copy in email newsletters for just computers. Some smartphones like the iPhone tend to enlarge any font that’s less than 12 points. This can cause newsletters to render improperly. At a minimum, keep newsletter body copy to 12 points. If you can do 14 points, that’s even better.

• Use Text-Based Phone Numbers: Some newsletters display phone numbers in the header as images. This is a big mistake. Most smartphones have the ability to click and call on text-based phone numbers. You’re missing out on an opportunity to possibly get phone calls if you save phone numbers as images.

• Shorten Headlines: Just like subject lines, you’ll want to keep any text-based headlines within your newsletter to fewer than 40 characters. It makes it easier to read on mobile devices.

• Space Out Clickable Items: To ensure that people click on the right links and buttons in your newsletter, space them out. Having clickable items too close together can cause people to accidentally click on the wrong items.

• Use Alt Tags for Images: Some mobile email programs block images from unknown senders. An alt tag is code that provides text information so a person can know what the images is just in case they can’t view it.

Most importantly…. TEST YOUR EMAILS on mobile devices. You’ll probably have some people at your business that have iPhone and Android smartphones. Send them test versions of the newsletter to see how they look.