Many brands put much of their marketing efforts into obtaining new customers—and understandably so. But acquisition isn't enough. Customers who make a one-time purchase won't necessarily come back for more. If you want customers to return, you have to make your brand memorable by giving them the experience they feel they deserve. Taking the extra steps to make your customers happy is the secret to making them loyal.

You can build customer loyalty in various ways, but email marketing is one of the most effective. That may sound surprising and counterintuitive to those of us who don't like spammy marketing emails. Yet, email is the No. 1 activity on mobile phones, and strategic email marketing—done effectively—is one of the best ways to retain a loyal customer base.

Here are seven tips to make sure your email program encourages retention and loyalty.

1. Know your customers

The first step in creating emails that build customer loyalty is to know your customers, AKA your audience. As well-written and persuasive as you might think your emails are, you won't attract customers if your emails don't speak directly to your audience.

One of the most effective ways to understand your customers is to build buyer personas. Tough an abstract representation of your ideal customer, a buyer persona is based on actual customer data and market research. To make your buyer personas seem like real customers, you should consider giving them a name, a gender, a job, a salary figure, and other relevant attributes that your target customers possess.

Hubspot's MakeMyPersona tool is a useful platform for beginning your buyer persona brainstorming. Once you create those personas, you can tailor your email messages accordingly.

2. Start from a clean slate

Your new and improved email campaigns should, of course, eventually target all your customers. But before you discard your former email strategy, test and assess your new email campaigns to make sure they produce results as expected.

The best way to do that is to aim for a fresh start: that is, target new campaigns at new customers who haven't yet formed an opinion about your product. That way, you'll be able to analyze customer responses solely in relation to the new campaign, and your analysis won't become convoluted by a mix of campaigns.

When you deploy your new campaigns to these new customers, compare their effects to the effects of your old campaigns on other customers, and check for improvements in conversion.

When you've determined what makes your campaigns most effective, gradually start implementing those new campaigns across more and more customers, including long-time customers, and phasing out older campaigns and blast emails.

3. Target individual segments

Your new campaigns and messages should be personalized and tailored to each customer type. Platforms such as Optimove let you hyper-target your customers, sorting them into segments based on real-time customer data.

Different customer types should receive different emails based on their specific needs and their customer status. For example, you might have one email directed at businesswomen age 30-40 who have abandoned their cart, and a different email directed at businesswomen age 30-40 who have only browsed the site.

Though 37% of marketers say list segmentation is the most challenging email marketing strategy, you can strategically craft your emails based on your detailed customer segments.