I agree with ClayButler. Getting traffic in the door is one thing. What you do with them next is important. You want to create a relationship, build loyal customers, customers that trust you and return to you. We spend enough time and money getting new customers, retaining them is easier and less expensive - but you need the right tools and to dedicate yourself to that means.

We use Boomerang email marketing for our email newsletters and promotions. We've seen return customer visits, purchases and revenue increase dramatically since we've implemented this program.

As for convincing your client, my suggestion is to try things on a trial basis. He's probably saying "show me the money." Email is pretty inexpensive, you can segment a portion of your list and track the results. Prove to him how it works on a test group and you'll be rolling out to the whole database in no time.