The following macros are currently defined by the Milter interface:
$j Text placed in the by clause of Received: header fields. In Messaging Server this is controlled by the RECEIVED_DOMAIN MTA option. If the option is not set, the official host on the local channel is used instead.
${client_addr} The IP address of the SMTP client, expressed as a dotted quad value. Only set when SMTP over TCP is being used.
$i Queue ID for the current message. Messaging Server generates a unique ID for each session; this ID is what appears in the $i macro.
${mail_addr} The MAIL FROM address for the current transaction.
${mail_host} The host part of the MAIL FROM address for the current transaction.
${rcpt_addr} A RCPT TO address for the current transaction.
${rcpt_host} The host part of the current RCPT TO address.