The right ESP (email service provider) can make all the difference in your marketingYour digital mailing list is a precious thing. But how you use it is as important as the number of email addresses it contains. Enter the email service provider (ESP), the online tool of choice for retailers looking to connect with core clientele. Popular ESPs share similar features: an easy-to-use interface, the ability to create multiple lists, and tools to track sent messages. But an ESP can be the difference between highly targeted marketing and sending emails into a vacuum. Here are a few best practices for marketing with ESPs. Pick a Winner Constant Contact is perhaps the most used ESP around; it was founded in 1995 and now counts more than a ­half-­million customers. Critics have likened the service to a slow-­moving giant, but it’s the industry standard. Gene Marks, president of CRM