7.3.2 Check Validity of Received:
The Received: header traces the succession of hosts that an email message passes
through. One technique used by spam messages is to create false Received: headers
This is the Title of the Book, eMatter Edition
Copyright ?© 2007 O??™Reilly & Associates, Inc. All rights reserved.
7.4 Relaying | 267
both to mask the real identity of the original sending host, and to divert blame to
some innocent site. One form of bad Received: header that appears in spam messages
looks like this:
Received: from ...............................................................
........................................................................
........................................................................
........................................................................
........................................................................!
This form of Received: header was popular with spam software for a few months,
then fell out of favor. The following rule shows one way of dealing with such headers:
LOCAL_RULESETS
H*: $>ScreenForDots
SScreenForDots
R $+ .......... $* $#error $: "553 Ten or more dots begin " $&{hdr_name} "header"
Here, the LOCAL_RULESETS part of your mc file begins withan unusual-looking H
configuration command. The H* is special (?§25.5.2 on page 1134) because it matches
all headers.
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