"It's hard to overestimate how useful a really good list can be-especially when it's been targeted to include the right groups of people," Cates says. People who are interested in only one product or aspect of your business or organization may not always be interested in every part. "Whether you are a pet store that wants to give a coupon to dog owners and not cat owners, or a nonprofit that wants to communicate with previous contributors but not volunteers, having separate lists so that you can tailor your email campaigns is a must," he advises.

You need a real sense of where your customers, clients, or supporters fit to effectively segment your lists. Cates' email marketing tips include thinking about what sort of campaigns you plan to send in the future, as well as what your customers want and expect from you. "This can be as easy as sending out a brief survey to find out who wants to be receiving what. Just be clear, and explain why you're asking these questions," he says. This sets expectations up front and will often result in a higher response rate. "Once you know how you want to segment your lists and know how you'll create them, you can work on filling them with subscribers."

If you need more customer data to properly segment lists, Cates recommends the use of a poll as a quick way to get people's opinions on a single topic. For customers, it's visual, it's interesting, and it takes just a second to answer, Cates says. As a result, you can use a poll to "help foster a sense of interaction, since those who answer can see what other customers have picked," he says. "Once you've got a good pool of responses, you can create new lists based on your results."