_smtp._srv.$&{client_addr}
Thus, if the lookup fails to get a ???1???, the reject text is used and the message is
rejected. If the lookup fails for a temporary (recoverable) reason the tempfail text is
used and the message??™s acceptance is deferred.
Note that, if the MTA mark proposal is revised at a later date, the literal _perm._
smtp._srv may need to be changed. If so, you may replace it by adding a third argument
to the feature declaration, such as _permit._srv:
FEATURE(`mtamark??, `reject??, `tempfail??, `_permit._srv??)
The default timeout for the lookup is five seconds. If that turns out to be too short
for your needs, you may increase it by defining the MTAMARK_TO mc macro:
define(`MTAMARK_TO??, `20??)
FEATURE(`mtamark??, `reject??, `tempfail??)
Note that the timeout must be defined before you declare the feature.
7.6.5 FEATURE(require_rdns)??”V8.14 and Later
When a client machine connects to your sendmail server, sendmail records the IP
address of the connecting client in the ${client_addr} macro (?§21.9.18 on page 810).
Next, sendmail looks up that IP address (performs a reverse DNS lookup of that
address) to find the client??™s hostname. The status of that lookup is stored in the
${client_resolve} macro (?§21.9.25 on page 814). This FEATURE(require_rdns)
rejects connections from clients for whom the reverse lookup fails.
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