in-addr.arpa. suffix to it. For
example:
123.45.67.8 would look up as ?†’ 8.67.45.123.in-addr.arpa.
The fourth rule detects the result of the lookup. If the workspace ends in a literal .FOUND,
the lookup was successful and the rule set returns a $#OK, which means that the message is
acceptable.
The last rule handles any lookup failure (including temporary failures). The envelope
sender is rejected with a temporary error, thus causing the sending site to retain the
message in its queue. If the IP address can be looked up in the future, no harm is done.
Otherwise, the message will eventually bounce.
The value returned by the dns-type database map is always a single item. If a host has
multiple MX, A, or AAAA records, a successful lookup will return only one suchrecord. In
the case of MX records, the lowest-cost record may not be returned.*
This dns-type database map can be used only if sendmail was built withth e NAMED_BIND
and DNSMAP compile-time macros defined (which they are by default).
This dns-type database map is used primarily by FEATURE(dnsbl) (?§7.2.1 on page 261) and
FEATURE(enhdnsbl) (?§7.2.2 on page 263). Both of these features use the -RA and -T
switches. FEATURE(enhdnsbl) also uses the -r5 and -a. switches. Beginning with V8.13,
* If you need to find the lowest-cost (or other preference) MX record, or multiple MX records, use the bestmx
database map instead (?§23.
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