The ${daemon_port} macro contains the value of the DaemonPortOptions=Port option (See this section) whenever mail is processed by the daemon listening on that port.

As distributed, this ${daemon_port} macro is not used in the configuration file. It is, however, available to you for use in designing your own particular rule sets. Note that a $& prefix is necessary when you reference this macro in rules (that is, use $&{daemon_port}, not ${daemon_port}).

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