Safe list: Safe lists are lists of e-mail addresses from people who have requested to receive messages and information about a specific topic. As you probably know, to deliver comments or advertisement via e-mail to others without their consent or authorization is called spamming and is illegal.
Also if you spam others do not expect to receive a reasonable response rate from them. What do I mean? I mean that you can send a message to millions of individuals, but if they are not interested in what you are selling and they didn’t requested that information from you, then you will probably make very few sales, plus you will receive a lot of complaints from hundreds of them.
Then what is the smart way to advertise using e-mail addresses?