Customized communications have the potential to reduce information overload and aid customer decisions, and the highly relevant products that result from customization can form the cornerstone of enduring customer relationships. In spite of such potential benefits, few models exist in the marketing literature to exploit the Internet's unique ability to design communications or marketing programs at the individual level. We develop a statistical and optimization approach for customization of information on the Internet. We use clickstream data from users at one of the top ten most tracked websites to estimate the model and to optimize the design and content of such communications for each individual. Our model is applied to the context of permission based email marketing, where the objective is to customize the design and content of the email in order to increase website traffic. Our analysis suggests that our content targeting approach can potentially increase the expected number of click-throughs by 62%.