Presto Vivace writes "Under the guise of fighting spam, five of the largest Internet service providers in the U.S. plan to start charging businesses for guaranteed delivery of their e-mails. In other words, with regular service we may or may not deliver your email. If you want it delivered, you will have to pay deluxe. 'According to Goodmail, seven U.S. ISPs now use CertifedEmail, accounting for 60 percent of the U.S. population. Goodmail--which takes up to 50 percent of the revenue generated by the plan--will for now approve only mail sent by companies and organizations that have been operational for a year or more. Ordinary users can still apply to be white-listed by individual ISPs, which effectively provides the same trusted status.'"
We warn the reader in advance that the proof presented here depends on a
clever but highly unmotivated trick.
-- Howard Anton, "Elementary Linear Algebra"