Personas provide a multi-dimensional method of targeting. They’re based, as the name suggests, on a projected persona for each customer ‘type’. Get it right, and personas can help you enormously in both predicting behaviour and personalising your communications. Personas are a powerful technique, and they’re increasingly used to improve the usability and customer centricity of communications.
If you're inviting readers to download an ebook, for example, and you have a picture of the ebook included in the email, don't just hyperlink the text next to the image telling people to "download it here." Hyperlink the ebook's picture, too. People are drawn to images much more commonly than text, and you want to give your email subscribers as many options to get your ebook as you can.
When you're using email as a marketing tool, you're working on a pretty personal basis. This isn't ‘drive-by' stuff -you're directly targeting customers from their inboxes. There's a huge amount of potential which comes with this kind of marketing... but you'll only reap that potential if you REALLY understand both the marketplace you're operating from, and the audience you're talking to.