When you build an opt-in list, you're creating one of the most valuable assets of your online business. Your customers and subscribers have given you permission to send them e-mail. That means:
You're giving them something they've asked for.
You're developing lifetime relationships with them.
The response is 100 percent measurable.
E-mail marketing is cheaper and more effective than print, TV or radio because it's highly targeted.
Anyone who visits your site and opts in to your list is a very hot lead. And there's no better tool than e-mail for following up with those leads.