Chapter 9. DNS and sendmail
DNS stands for Domain Name System. A domain is any logical or physical collection of related hosts or sites, such as example.gov or www.example.gov.
What’s New with V8.13
The
dnsblfeature (7.2.1[3ed]) no longer uses thehostdatabase-map type to look up addresses. Instead, it uses thednsdatabase-map type (Section 9.1.1 [V8.13]).The
DNSBL_MAP_OPTmcmacro (Section 9.1.1 [V8.13]) has been added so that you may tune the database-map flags used with thednsblfeature.The
check_relayrule set (7.1.1[3ed]) is now called with the value of${client_name}macro (21.9.20[3ed]), allowing it to deal with bogus DNS entries (Section 9.1.2 [V8.13]).
Feature dnsbl Uses dns Database-Map
The dnsbl feature (7.2.1[3ed]) is used
to
enable the blocking of email
from open relay sites, dial-up sites, or known spamming sites. It
does so by invoking the RBL technique, which is discussed in
7.2[3ed].
Prior to V8.13, the dnsbl feature employed the
host database-map type
(23.7.9[3ed]) to look up addresses.
Beginning with V8.13, this feature now uses the
dns database-map type
(23.7.6[3ed]).
The default declaration for the dns database-map
for this feature looks like this:
Kdnsbl dns -R A -T<TMP>
If you wish to change the type of the lookup, you may redefine the
dns -R A part of the expression:
define(`DNSBL_MAP´, `dns -R TXT´) FEATURE(dnsbl, ...)
Here, the DNSBL_MAP redefines the
lookup
so that it performs TXT record lookups instead of
A record lookups. Note that
DNSBL_MAP must be defined ...