sendmail, 4th Edition

${if_family}

The network family of the receive interface V8.10 and later

When sendmail first starts up as a listening daemon, it binds to a port on all interfaces or on a particular interface (DaemonPortOptions=Addr= on page 994). It then waits to accept connections from hosts or programs that wish to route mail through it. Those hosts or programs are called “clients,” and when they initiate a connection, it is called a client connection.

When a client connects to the local machine, sendmail records the local IP address of the connected-to interface in the ${if_addr} macro (as described earlier) and the family of that address in this ${if_family} macro. The family is a text representation of the integer value that represents the family, as defined in sys/socket.h. If the connection is from the local host, the ${if_family} macro is undefined. A value of 2, for example, could represent the AF_INET family.

${if_family} is available for use in rule sets, and can be useful for rejecting spam or restricting connections to particular addresses. Note that a $& prefix is necessary when you reference this macro in rules (that is, use $&{if_family}, not ${if_family}).

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