Below are the SMTP commands/responses, and the test-milter output showing that the second "DATA" event is reported with the correct queue ID.
Wietse $ telnet 127.0.0.1 smtp Trying 127.0.0.1... Connected to 127.0.0.1. Escape character is '^]'. 220-wzv.porcupine.org ESMTP Postfix 220 wzv.porcupine.org ESMTP Postfix ehlo wzv.porcupine.org 250-wzv.porcupine.org 250-PIPELINING 250-SIZE 10240000 250-VRFY 250-ETRN 250-ENHANCEDSTATUSCODES 250-8BITMIME 250-DSN 250 SMTPUTF8 mail from:<> 250 2.1.0 Ok rcpt to:<wietse@localhost> 250 2.1.5 Ok data 354 End data with <CR><LF>.<CR><LF> blah . 250 2.0.0 Ok: queued as 8E063A009F mail from:<> 250 2.1.0 Ok rcpt to:<wietse@localhost> 250 2.1.5 Ok data 354 End data with <CR><LF>.<CR><LF> blah . 250 2.0.0 Ok: queued as 2751DA009E quit 221 2.0.0 Bye Connection closed by foreign host. $ exit exit $ ./test-milter -d 1 -p inet:9999@127.0.0.1 test_connect localhost AF_INET (127.0.0.1:44670) macro: j="wzv.porcupine.org" macro: v="Postfix 3.3-20170212" macro: {daemon_addr}="127.0.0.1" macro: {daemon_name}="wzv.porcupine.org" test_reply 0 test_helo "wzv.porcupine.org" macro: j="wzv.porcupine.org" macro: v="Postfix 3.3-20170212" macro: {daemon_addr}="127.0.0.1" macro: {daemon_name}="wzv.porcupine.org" test_reply 0 test_mail "<>" macro: j="wzv.porcupine.org" macro: v="Postfix 3.3-20170212" macro: {daemon_addr}="127.0.0.1" macro: {daemon_name}="wzv.porcupine.org" macro: {mail_addr}="" macro: {mail_host}="wzv.porcupine.org" macro: {mail_mailer}="local" test_reply 0 test_rcpt "<wietse@localhost>" macro: j="wzv.porcupine.org" macro: v="Postfix 3.3-20170212" macro: {daemon_addr}="127.0.0.1" macro: {daemon_name}="wzv.porcupine.org" macro: {mail_addr}="" macro: {mail_host}="wzv.porcupine.org" macro: {mail_mailer}="local" macro: {rcpt_addr}="wietse@localhost" macro: {rcpt_host}="wzv.porcupine.org" macro: {rcpt_mailer}="local" test_reply 0 test_data macro: i="8E063A009F" macro: j="wzv.porcupine.org" macro: v="Postfix 3.3-20170212" macro: {daemon_addr}="127.0.0.1" macro: {daemon_name}="wzv.porcupine.org" macro: {mail_addr}="" macro: {mail_host}="wzv.porcupine.org" macro: {mail_mailer}="local" macro: {rcpt_addr}="wietse@localhost" macro: {rcpt_host}="wzv.porcupine.org" macro: {rcpt_mailer}="local" test_reply 0 test_header "Message-Id" "<20170329233029.8e063a0...@wzv.porcupine.org>" macro: i="8E063A009F" macro: j="wzv.porcupine.org" macro: v="Postfix 3.3-20170212" macro: {daemon_addr}="127.0.0.1" macro: {daemon_name}="wzv.porcupine.org" macro: {mail_addr}="" macro: {mail_host}="wzv.porcupine.org" macro: {mail_mailer}="local" macro: {rcpt_addr}="wietse@localhost" macro: {rcpt_host}="wzv.porcupine.org" macro: {rcpt_mailer}="local" test_reply 0 test_header "Date" "Wed, 29 Mar 2017 19:30:20 -0400 (EDT)" macro: i="8E063A009F" macro: j="wzv.porcupine.org" macro: v="Postfix 3.3-20170212" macro: {daemon_addr}="127.0.0.1" macro: {daemon_name}="wzv.porcupine.org" macro: {mail_addr}="" macro: {mail_host}="wzv.porcupine.org" macro: {mail_mailer}="local" macro: {rcpt_addr}="wietse@localhost" macro: {rcpt_host}="wzv.porcupine.org" macro: {rcpt_mailer}="local" test_reply 0 test_header "From" "MAILER-DAEMON" macro: i="8E063A009F" macro: j="wzv.porcupine.org" macro: v="Postfix 3.3-20170212" macro: {daemon_addr}="127.0.0.1" macro: {daemon_name}="wzv.porcupine.org" macro: {mail_addr}="" macro: {mail_host}="wzv.porcupine.org" macro: {mail_mailer}="local" macro: {rcpt_addr}="wietse@localhost" macro: {rcpt_host}="wzv.porcupine.org" macro: {rcpt_mailer}="local" test_reply 0 test_eoh macro: i="8E063A009F" macro: j="wzv.porcupine.org" macro: v="Postfix 3.3-20170212" macro: {daemon_addr}="127.0.0.1" macro: {daemon_name}="wzv.porcupine.org" macro: {mail_addr}="" macro: {mail_host}="wzv.porcupine.org" macro: {mail_mailer}="local" macro: {rcpt_addr}="wietse@localhost" macro: {rcpt_host}="wzv.porcupine.org" macro: {rcpt_mailer}="local" test_reply 0 test_body 6 bytes macro: i="8E063A009F" macro: j="wzv.porcupine.org" macro: v="Postfix 3.3-20170212" macro: {daemon_addr}="127.0.0.1" macro: {daemon_name}="wzv.porcupine.org" macro: {mail_addr}="" macro: {mail_host}="wzv.porcupine.org" macro: {mail_mailer}="local" macro: {rcpt_addr}="wietse@localhost" macro: {rcpt_host}="wzv.porcupine.org" macro: {rcpt_mailer}="local" test_reply 0 test_eom macro: i="8E063A009F" macro: j="wzv.porcupine.org" macro: v="Postfix 3.3-20170212" macro: {daemon_addr}="127.0.0.1" macro: {daemon_name}="wzv.porcupine.org" macro: {mail_addr}="" macro: {mail_host}="wzv.porcupine.org" macro: {mail_mailer}="local" macro: {rcpt_addr}="wietse@localhost" macro: {rcpt_host}="wzv.porcupine.org" macro: {rcpt_mailer}="local" test_reply 0 test_mail "<>" macro: j="wzv.porcupine.org" macro: v="Postfix 3.3-20170212" macro: {daemon_addr}="127.0.0.1" macro: {daemon_name}="wzv.porcupine.org" macro: {mail_addr}="" macro: {mail_host}="wzv.porcupine.org" macro: {mail_mailer}="local" test_reply 0 test_rcpt "<wietse@localhost>" macro: j="wzv.porcupine.org" macro: v="Postfix 3.3-20170212" macro: {daemon_addr}="127.0.0.1" macro: {daemon_name}="wzv.porcupine.org" macro: {mail_addr}="" macro: {mail_host}="wzv.porcupine.org" macro: {mail_mailer}="local" macro: {rcpt_addr}="wietse@localhost" macro: {rcpt_host}="wzv.porcupine.org" macro: {rcpt_mailer}="local" test_reply 0 test_data macro: i="2751DA009E" macro: j="wzv.porcupine.org" macro: v="Postfix 3.3-20170212" macro: {daemon_addr}="127.0.0.1" macro: {daemon_name}="wzv.porcupine.org" macro: {mail_addr}="" macro: {mail_host}="wzv.porcupine.org" macro: {mail_mailer}="local" macro: {rcpt_addr}="wietse@localhost" macro: {rcpt_host}="wzv.porcupine.org" macro: {rcpt_mailer}="local" test_reply 0 test_header "Message-Id" "<20170329233044.2751da0...@wzv.porcupine.org>" macro: i="2751DA009E" macro: j="wzv.porcupine.org" macro: v="Postfix 3.3-20170212" macro: {daemon_addr}="127.0.0.1" macro: {daemon_name}="wzv.porcupine.org" macro: {mail_addr}="" macro: {mail_host}="wzv.porcupine.org" macro: {mail_mailer}="local" macro: {rcpt_addr}="wietse@localhost" macro: {rcpt_host}="wzv.porcupine.org" macro: {rcpt_mailer}="local" test_reply 0 [further events omitted]