There's a strong chance that many of your customers check their emails on their mobile devices. That's why it's important to design your emails to effectively render on mobile devices so your message remains clear and effective.
Here are some email guidelines to keep in mind to make sure you're getting through, no matter how small the screen. 
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Keep It Brief. Keep your contact info, subject line, and content short and sweet so the recipient can easily view your message.
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Be Interesting. Your recipients still use their computers to view feature-rich emails and act on the messages they've received on their phones. Make sure your message is compelling enough to get flagged for follow-up when they're back at their computers.
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Try MIME. Make sure your email platform has multi-part MIME capabilities. This allows each individual mail client to interpret your email and display it however it can render. Using this capability provides the benefits of rendering an HTML version on a recipient's desktop while most mobile phones render emails as text.
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Test! See how your message renders on different mobile devices to be sure the version you're sending effectively communicates your message, no matter how it renders.
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Stay Up-To-Date. Be aware of innovations and changes in the mobile device arena so you can tweak your design for maximum deliverability as needed. Look to trade groups like the Direct Marketing Association and the Mobile Marketing Association for best practices in delivery of email to mobile devices.
Since mobile devices are still in their infancy stages, there are no set "best practices" to effective rendering across all mobile devices, but there are differing opinions whether HTML or text is a safer bet. Our advice? Know your audience, use multi-part MIME, and test, test, test!
