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If you use email, it's likely that you've recently been visited by a piece of spam ‚an unsolicited , unwanted message, sent to you without your permission.  If you manage an email system, it's almost certain that you've had to help your users avoid the deluge of unwanted email.
System administrators pay for spam with their time. The Internet's email system was designed to make it difficult to lose email messages: when a computer can't deliver a message to the intended recipient, it does its best to return that message to the sender. If it can't send the message to the sender, it sends it to the computer's postmaster ‚because something must be seriously wrong if both the email addresses of the sender and the recipient of a message are invalid.
The well-meaning nature of Internet mail software becomes a positive liability when spammers come into the picture. In a typical bulk mailing, anywhere from a few hundred to tens of thousands of email addresses might be invalid. Under normal circumstances these email messages would bounce back to the sender. But the spammer doesn't want them! To avoid being overwhelmed, spammers often use invalid return addresses. The result: the email messages end up in the mailboxes of the Internet postmasters, who are usually living, breathing system administrators.
System administrators at large sites are now receiving hundreds to thousands of bounced spam messages each day. Unfortunately, each of these messages has to be carefully examined, because mixed in with these messages are the occasional bounced mail messages from misconfigured computers that actually should be fixed.
As the spam problem grows worse and worse , system administrators are increasingly taking themselves off their computers' "postmaster" mailing lists. The result is predictable: they're deluged with less email, but problems that they would normally discover by receiving postmaster email are being missed as well. The Internet as a whole suffers as a result.
Although there are many important ways to reduce spam ‚including obscuring email addresses, complaining to spammers' service providers, and seeking legal and legislative relief ‚few remedies are as immediately effective as filtering email messages on the basis of content and format, and few filtering systems are as widely used and well maintained as SpamAssassin .
This book is for mail system administrators, network administrators, and Internet service providers who are concerned about the growing toll that spam is taking on their systems and their users and are looking for a way to regain some control or reduce the burden on their users.
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