Email marketing. Yawn. Endless digital marketing agencies will try and sell you that email is passe and to succeed as a small business you need to have a robust Snapchat and Instagram strategy. Well, plainly, they're wrong. Unless, of course, your business is only focused on teens.

Email marketing is the best way to get the most sales for each and every marketing dollar you spend. E-consultancy found that the ROI on email outperformed every other channel for small businesses, with a staggering return on investment of 73 percent.

The other big secret of the industry? You don't actually need a costly email management program or CRM with all the bells and whistles. Until you have an email list with thousands and thousands of customers and the need to do advanced segmentation, low-cost or even free software should fit you just fine.

And yet 60 percent  of small business owners don't use email marketing.

If that includes you, pay attention to these five ways you could be using email--and growing your business.

Use a simple--yet powerful--online tool: a CRM.

A customer relationship management (CRM) tool does more than keep a list of your current and potential customers. A lot more. It can track things about them that allow you to offer content and offers that are most relevant to them--and most likely to get sales for you.

Understand who your customers are.

You have different types of customers, and they have very different problems and needs. Some have been buying from you for years, others have visited you once. Some are buying for a business of their own, others for themselves. So why talk to them like they are all the same? You probably already know a few types of customers unique to your business, so now think about what the key differences are, and what messages will be most relevant to them--and most likely to get them to engage with you.

Create interesting content.

All of us get annoying emails--offers for things we don't want, and even total spam. This is what makes it easy to overlook email as such an effective channel. Try to keep the style conversational and "folksy". Using an anecdote to highlight a real life customer relationship usually grabs the reader's attention.

The key is, you have to write good content. That means information that's relevant and interesting. Don't get caught in the trap of sending something out because it's "on the schedule". Bad content will make customers lose interest and lose trust in you.

Keep it simple.

With 269 billion emails sent every day, people have a lot competing for their attention. Because of that, people skim: the average time people spend on a promotional email is just 15-20 seconds. Can your message get through in that time? If not, it's time to simplify, simplify, simplify.

Don't forget the call-to-action (CTA).

Make it very easy for customers to take action. Do you want them to buy something? Have a big BUY button. Do you want them to read more about a product you're advertising? Have a professional photo of the product and a big LEARN MORE button.

Bottom line, email marketing is an oldie-but-goodie, and an important  for you to engage with your customers--and increase your sales.