Use the email addresses wisely. Treat them like gold, because they are. Once you have the email address, you must keep it updated. Like their work or home addresses, customers do change their email addresses as well. About the only good thing about an outdated email address is that it bounces back to you immediately, instead of direct mail where it could take several weeks and trips around the globe to discover it's wrong.
Email is cheaper too.
The point here is that customer email addresses need to be updated and kept current. Dealers need to constantly research if their customers' info is correct and should update it when it changes, immediately. You just need the right tools. Mining for customers may be easy to say, but as all dealers know, it's a difficult process. However, by collecting customer emails addresses, dealers have a new tool to strike it rich through email promotions.