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7.6 Spam Suppression Features | 295
Here, ms_pause sets the default number of milliseconds to pause for any host,
domain, or IP address that is not found in the access database.
Note that any detection of slamming will result in no Milter being called, and will
prevent checkcompat() from being called.
7.6.4 FEATURE(mtamark)??”V8.13 and Later,
Experimental
One way to reduce spam email is to set up a mechanism for marking each MTA as an
MTA. To illustrate, consider a spam email received from a host with the IP address
192.168.123.45, that claims to be a legitimate MTA. Currently, sendmail can only
look up that address using various open relay sites to see whether the IP address corresponds
to an open relay, and to reject the message if it does. Under the MTA mark
proposal,* sendmail can look up a special TXT record associated withth at address to
see whether that IP address is marked as that of an MTA. You may emulate this
lookup using dig(1) like this:
% dig txt _perm._smtp._srv.45.123.168.192.in-addr.arpa
Here, the _perm._smtp._srv is a literal defined by the MTA mark proposal. The
45.123.168.192 is the original IP address reversed, and the in-addr.arpa is the special
domain used to treat IP addresses like domain names.
This lookup can return one of two possible TXT records. A ???1??? means that this IP
address is that of an MTA.
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