A ???0??? (or any other character) means that this IP address
is not that of an MTA. Mail from an unmarked MTA may, under this proposal, be
rejected.
Once this proposal is in place, spam sites will no longer be able to send spam email
via hijacked PCs, via hired PCs, or via worms implanted in PCs. When spam email
does arrive, you will be certain that it is from a marked MTA and only from a marked
MTA. Then, by blocking email from that IP address, you will be able to turn off that
site??™s spam at the source.
This experimental FEATURE(mtamark) enables use of this proposal, but it should not
be used unless you are willing to experiment. It is declared like this:
FEATURE(`mtamark??, `reject??, `tempfail??)
Here reject is either a rejection message of your own or, if it is omitted, a default
that looks like this:
550 Rejected: $&{client_addr} not listed as MTA
* As of this writing, see http://mtamark.space.net/draft-stumpf-dns-mtamark-04.txt.
This is the Title of the Book, eMatter Edition
Copyright ?© 2007 O??™Reilly & Associates, Inc. All rights reserved.
296 | Chapter 7: How to Handle Spam
Here, the ${client_addr} macro (?§21.9.18 on page 810) contains the IP address of
the connecting host that was looked up.
The second argument, the tempfail, is either a literal t or a temporary failure message
of your own. The t causes the following default to be used:
451 Temporary lookup failure of _perm.
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