We are dealing with tens of millions of people already. In the next few years it will be in the hundreds of millions. Probably only a small fraction. Niche marketing is the way to go. Focus on an area, and you will thrive.
Most people take e-mail for granted, it is an extremely valuable tool.
It means use the power of e-mail to your advantage. I have e-mailed and received responses from major publications and high level management personnel. I know via other communications I would not have gotten a response. These people are now a part of my community and many are now customers. You do have access to many experts via e-mail.