One might also distinguish research and education from other uses but I am going to ignore that distinction for the present in the hope it won't prove useful. It is no longer adequate to base guidelines for conduct purely on the basis of who pays for the underlying network or computer systems resources. Even if that was once sensible, the diversity of constituents of the Internet makes it a poor basis for formulating policy. Thus, guidelines for conduct have to be constructed and motivated in part on the basis of self-interest. Many of the suggestions below are based on the theory that enlighted self-interest can inform and influence choices of behavior.
Mailing lists are like common property in information space.
Often such lists are set up by mutual agreement among the list members and dedicated to a particular purpose. I fully recognize the problem of definition here, especially in dealing with pornography. Advertising Advertising is permitted and even encouraged on the Internet but advertisers are advised to give thought to how the Internet resources can best be applied for this purpose. As the history section attempts to say, this constraint has largely evaporated since 1988 as policies supporting much broader use began to evolve. Nonetheless, sensible advertisers will be sensitive to the way in which their information is received by potential clients, so as to maximize positive gains.