Dive summary:

• By year end, more emails will be opened on mobile devices than desktop, so it is essential for marketers to provide a good email experience for both desktop and smartphones.
• The mobile use-case is different than desktop, as your audience very often is in a hurry.  Because of this, simplicity is key in design.  Keep the email narrow, the buttons big, and text larger.
• Images need to be as lean as possible for quick viewing.  Remember, your audience is in a hurry so they aren't going to forgive long image load times.
• Be concise, and make the call-to-action front and center.  Note that the call to action doesn't always have to be something they have to do NOW, but for example an "email me later" call to action for a white paper form can save your prospect time and is allows your team to follow up.

From the article:

Mobile is the technology with the highest audience penetration rate globally, and with smartphone ownership on the rise, mobile email marketing is going becoming increasingly important. With that said, the term "mobile email campaign" is a misnomer. The first and foremost concept email marketers need to embrace is that there is really no such thing as a mobile email campaign in the strictest sense. Emails are sent to email addresses, and it is the recipients alone who decide whether to read those emails on their mobile phones or on their desktop computers. Consumers' preferences can and wil...