Michael E. of Mobile Marketing Watch offers something of a primer for advertisers today as he explains why email marketing still matters in 2014. The piece cites a prediction from eMarketer that the number of email users worldwide will grow from 2.4 billion this year to 2.8 billion by 2017, and notes that wearable devices and other next-generation devices will enable us to access email in a variety of new ways. The writer then offers some basic tips for email marketers: Make your email campaigns relevant to consumers, deliver your messages at the most effective time, present a call to action and monitor the results.

But the piece fails to mention maybe the biggest mistake email marketers make — delivering emails that are difficult or even impossible to read on a phone. The majority of big-brand, business-to-consumer emails are opened on smartphones, according to Movable Ink. But I’m constantly amazed at the number of emails I get from big businesses that are simply unreadable on a high-end smartphone — images often don’t come through, only a fraction of the text is presented, or reading the entire content requires a ridiculous amount of scrolling. Ever-increasing smartphone penetration rates have laid the foundation for email marketers to engage with on-the-go users in creative, innovative ways. It’s shocking that so many companies still fail to do so at the most basic levels.