An email read on a BlackBerry might look very different than it would on an Apple iPhone or a Palm Treo. This is because the world of mobile email is like the Wild West: There are few rules; anything goes.

The increasing popularity of mobile devices presents a particular challenge for b2b email marketers. "Businesspeople are certainly checking business emails on mobile devices more than consumers are checking their personal emails," said Julie M. Katz, an analyst at Forrester Research. "B2b marketers have to be cognizant of this when designing their messages."

The plethora of mobile devices currently on the market adds to marketers' challenges, said Jordan Ayan, president of SubscriberMail. "The biggest challenge marketers face is that they must come to terms with the fact that they have no control over which email client people will be viewing their messages on," he said.

Unfortunately, Katz said, there are no official best practices for designing for the mobile market. Still, there are some steps marketers can take when sending emails to customers and prospects using such devices:

• Define your audience. You don't have to make a huge design overhaul if your audience isn't using mobile devices yet and doesn't plan to in the immediate future. Ayan suggested polling your audience about their mobile device use. In addition, make sure your opt-in materials have a field in which new subscribers can identify how they will be reading your messages. Once you know you have a large percentage of mobile users, then you may want to do more than just optimize your current messaging, he said.

  "If you've got a big mobile audience, you can let people choose how they want to receive your messages," he said. "Let them say, `I want to receive messages on my mobile device,' and then move them to a new list of mobile-only recipients."

  These recipients would get messages that are completely optimized for the medium, with short, bulleted snippets of text and a complete absence of images.

• Create a text-only version. You can make sure your email message renders as text-only by designing and sending messages using the multipart MIME standard, said Melissa Read, VP-research and innovation at Spunlogic, an interactive agency. "Fifty percent or more of mobile emails are rendered as text when sent as multipart MIME, making it easier to control the look and feel in the mobile inbox," she said.

  You can also provide a link at the top of your message that links mobile users to a text-only page.

• Keep it short. Subject lines and page widths are much narrower in the mobile world, said Eric Groves, senior VP-sales and business development at Constant Contact, a provider of email marketing software. "Subject lines on PC-based email clients are typically 30 to 45 characters. You have 20 or less to work with on a mobile device," he said. "A standard email width is about 600 pixels wide. On a mobile device,you're lucky if you get 120 pixels."

  This means that the first three words in the subject lines are crucial—and should contain the brand or product name. Plus, even if the majority of a message renders "above the fold" in an email client, that message is going to lose impact in a mobile device unless you design it carefully. The reason: People usually don't scroll when viewing their emails on a smaller device.

  "It really takes you back to basics," Groves said. "You've got to become more succinct, and copy has to be more valuable at the top."

• Include a phone number. Most smartphones and PDAs turn telephone numbers into actionable objects; users can click on the numbers and be connected instantly. This allows marketers to use a telephone number as a call to action, said Morgan Stewart, director of research and strategy at ExactTarget, a provider of email marketing software and services. Stewart suggested using a separate phone number so you can track which calls result from your email marketing. "You can send them through to a sales rep," he said. "That's a more realistic mobile call to action."

• Do some real-world testing. Even if you don't have a huge marketing budget, you can still test your design by running it past five to 10 employees or colleagues, all of whom use different mobile devices, Read said. "Test users while [they are] walking or doing other physical tasks … common situations in which the device will be used," she said. "What I find is when there is a serious problem, results tend to trend after five or six people."

• Forget open rates. The more people read your messages on mobile devices—most of which don't display images—the worse your open rates will be. Open rates rely on image rendering, so you'll need to find creative ways to track your messages' reach, Stewart said. "Think about taking people to optimized landing pages," he said.

  Groves suggested sending out surveys, too. "You need a way for them to tap you on the shoulder," he said.

• Consider hiring a mobile-centric email service provider. Last year, many of the major ESPs started branching out and incorporating mobile marketing into their product portfolios, Forrester's Katz said. "These ESPs can provide ways for marketers to set up campaigns so people can self-select mobile versions," she said. "This year we'll start seeing even more adoption as ESPs continue partnering with mobile providers to expand their offerings."