The sendmail program can listen for (await) inbound connections on more than one interface, where each interface can employ any one of five possible protocol families. Possible families are inet for AF_INET, inet6 for AF_INET6, iso for AF_ISO, ns for AF_NS, and x.25 for AF_CCITT. The value stored in this ${daemon_family} macro is taken from the DaemonPortOptions=Family option (See this section) whenever a message is processed by rule sets, and reflects the family of the interface upon which the inbound connection was received.

This ${daemon_family} macro is not used in the rule sets supplied with sendmail. It is, however, available for your use when designing custom rule sets. Note that a $& prefix is necessary when you reference this macro in rules (that is, use $&{daemon_family}, not ${daemon_family}).

${daemon_family} is transient. If it is defined in the configuration file or in the command line, that definition can be ignored by sendmail.