Large mailings of paper advertisements to home mailboxes, while inexpensive, do add up to a considerable expense. Large-scale emailings, however, can be done with little more than a computer and an internet connection. Due to the minimal expense associated with such large-scale emailing, potential profits can be quite large. Even at the incredibly low rate of responses, the expense of the messages is easily recovered.
A primary problem with spam email, therefore, is its volume. According to current estimates, approximately 95% of email is spam. This means that only 1 out of every 20 emails (i.e. 5%) is a substantive, non-spam mailing. Whether one considers this from the perspective of consumers, internet access providers, or the internet "system" as a whole, this volume of spam email requires a burdensome allocation of time, attention, and resources. This burden can be viewed as a non-consensual tax paid by all users alike.
An additional problem with spam email may be its content. Not only are spam emails unwanted solicitations, but they may advertise any of the following: pornography, services or products of questionable legality, work-at-home scams, chain letter scams, credit repair scams, loan grant scams, or similarly shady subjects.