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.
Make your offers feel relevant. If you offer people something they don’t think is relevant for them, they also think you don’t know them or understand their situation. Segmenting people based on their interests, problems, company sizes, and other things can help with that a lot. But it’s not enough. Your offer might be a perfect fit for them, but how you present it has to be a fit, too. Focus on describing their problems, how they’ll use the product or service, and what they will have in the end. Don’t talk about it from your perspective. No one really cares what you think about your product as much as they care about what they’ll get from it.

Send people content they want. Email newsletter services offer features like groups and segmentation to help you make your content relevant to the people reading it. If you're sending different emails for different groups (for example, a nonprofit might send separate emails to volunteers, donors, and the board of directors), then you can ask people to check a box to join a particular group on your signup form. Segmentation allows you to target certain subscribers on your list without assigning them to group. If your store is having a sale, then you could send a campaign only to people near a particular zip code, because subscribers who live in other parts of the world don't need to know about it. You can also segment by activity, email clients, e-commerce data, and more. Sending relevant content will keep your readers engaged, and engaged readers look forward to your newsletter and share it with friends.
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.