DNS stands for the Domain Name System protocol. DNS provides access to information about host names and addresses. DNS is covered fully in Chapter 9.

This DNSMAP compile-time macro, when defined with V8.12 sendmail and above, allows you to look up host and address information inside your configuration file using the dns database map type (dns). You enable the dns database map type in your Build m4 file like this:

APPENDDEF(`conf_sendmail_MAPDEF', `-DDNSMAP=1')

This definition will silently fail if you do not also define NAMED_BIND (NAMED_BIND) to include general DNS support inside sendmail. Normally, NAMED_BIND is defined by default, so that should not be a problem.

If you wish to use the enhdnsbl feature (Section 7.2.2) for improved spam screening, you must define this DNSMAP compile-time macro when building sendmail.

If you are running a precompiled sendmail binary, you can use the -d0.1 debugging command-line switch (-d0.1) to determine if DNSMAP support is included (if it appears in the list, support is included).