This of course is statistics. But what it says to you is that 485 people will not be ready without a measure of coaxing and prodding from you to mailing list purchase something. The common phrase that most Internet Marketers use is "The money is in the list" and I agree with them. You will however have to ensure that your list is made up of people who are interested in what you offer and have a desire for the outcome you provide.
If you send out an email blast or a direct mail campaign that never gets opened, you technically have no list to speak of. The desire must be there on the part of your subscribers to take action when your name is in front of them. How responsive mailing list your mailing list subscribers are depends on how well you develop your relationship with them and how much you understand who your prospects are.
You will get about as close to a deal as the Wolf man at a high school prom. Regardless of what kind of Internet Business you are mailing list starting, having your own mailing list is a must. No exceptions. The greatest reason to develop a responsive mailing list is the insurance it gives you in times of crisis and change. If you can go to your list and offer them a solution to perceived external threats, whether it's health, money or relationships; you will be the person that they turn to because you have a history with them.