This is real simple. Have one. And contact your mailing list once a month with news. Don’t cut corners on this either, a newsletter is where you’ll see the greatest impact on sales. All the tweets and facebook posts about a new album out for sale won’t equal the results of a well crafted newsletter, so spend money on a mailing list service provider that can help you design a rich looking email and provide analytics and tracking capabilities so you can measure the effectiveness of your newsletters and make adjustments where need be.