This goes right along with customer service. You would need to use a CRM tool to implement such an important part of your marketing plan. Zoho is a great CRM tool we recommend to our clients.  You should keep track of all the orders placed by your customers as well as abandoned shopping carts by your prospects. You can then use this information to send targeted marketing pieces, via e-mail or snail mail, that directly relate to the interests of your customers. This is a very intricate part of running your online business. Your best customers are the ones you satisfied in the past.