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Postfix: The Definitive Guide by Kyle D. Dent

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Chapter 11. Blocking Unsolicited Bulk Email

Unsolicited Bulk Email (UBE), also referred to as Unsolicited Commercial Email (UCE), is commonly called spam. Spamming is the practice of sending mass mailings to large numbers of people who have had no prior relationship with the sender and who didn't ask to receive such mail. Spam exists because it's so cheap to send. The incremental cost of adding even hundreds of thousands of recipients to a mailing is relatively small, so spammers target as many email addresses as they possibly can. This chapter looks at the problem of spam and the tools Postfix provides to help limit the consequences.

The Nature of Spam

There is a decidedly dishonest component to most spam. Spammers make no effort to match message content with a recipient's interests, and their messages frequently lie, claiming that the recipient has an association with the company or its partners or in some way requested information. Messages are sometimes designed to look like an actual exchange between two people that was mistakenly misdelivered in the hopes of sparking interest in some product or service.

Spam frequently offers instructions to opt out from receiving more messages; however, in many cases this is simply a subterfuge on the part of the spammer to confirm that your email address is good. By replying to such messages, you confirm that your address is a legitimate one. Following the directions provided will more than likely cause your address to be added to more spammer ...

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