For many businesses, landing new customers is the easy part. It's getting them to come back that proves tricky. Continuing to give them useful content via blog posts, tweets and Facebook posts are great tactics in a multifaceted strategy, and email newsletters are an important part as well. They can announce promotions that drive sales and give customers content they might otherwise not receive.
Email newsletters are also a way to gain new customers. A blog post or landing page could have a call to action at the end enticing customers to sign up for the newsletter. From there, it should only be a matter of time before a prospective customer converts into an actual customer.