I was receiving daily, unsolicited mail from Encyclopædia Britannica. No matter what I did, their mail kept on coming. "Unsubscribe" was useless. My ISP wrote to me that they were of the worst sort. I came up with a solution which, for me anyway, was original. Every time I received their mail, I rerouted it permanently to an Encyclopædia Britannica office or executive. Ultimately they were receiving an avalanche of their own mail. It might not have worked, but it did. Britannica put a stop to this unsolicited intrusion.