According to one study by Jupiter Research, sending marketing communications that are more relevant to your audience could increase net profits an average of 18 times – a powerful argument for the benefits of segmentation.

Many companies don’t segment their email marketing lists because there are virtually no incremental costs for sending the same message to everyone. But as more and more customers suffer from email overload, continued relevancy is key to maximizing your opt-in list.

How do you go about segmenting an email list? Here are a few possibilities:

* Surveys. Perhaps the best way to find out what people are interested in is to ask. As soon as people sign up to receive your emails, send a welcome note with a short survey asking what topics they’d like to receive information on.

* Zip codes. One of our clients is at maximum capacity in March, April and May, but could use more business from Southern states in January and February. After spinning off a separate email list of customers in just those zip codes, we’ll step up promotions to the right people at the right time.

* Links clicked. It’s likely that anyone who clicks on a link in an email promotion is more engaged than someone who doesn’t. What’s more, if you track the links that your email readers click on, you can glean information about what interests them. For instance, if you include a link to a list of shade-loving plants, you can bet that anyone who clicks on it would be interested in related emails, like a promotion for astilbe or hosta.

If you’re starting to see open rates decline or opt-outs rise, consider segmenting your email list. Once you have, you may find that you’ll be able to email the “cream of the crop” more frequently than before without jeopardizing the rest of your mailing list.