Hi, (I believe I have found the problem here and it is unrelated to postfix, but I would like to confirm a couple of things that are a bit hazy in the docs. After googling a lot yesterday, this may be a useful find for someone in the future.)
I got header checks working, but ran into the Catch-22 that the subject check would not pass for outgoing email, so I found the section of the manual titled as the subject of this email. Note that this may be impacted by the effect of the other topic I have posted on "spontaneous appearance...". I set up master.cf as described in that section: 1.2.3.5:smtp inet n - n - - smtpd 1.2.3.4:smtp inet n - n - - smtpd -o receive_override_options=no_header_body_checks 127.0.0.1:smtp inet n - n - - smtpd -o receive_override_options=no_header_body_checks pickup fifo n - n 60 1 pickup -o receive_override_options=no_header_body_checks After some time, I figured out how (I believe, I'm a C programmer, not a great admin, so please bear with me) to define 1.2.3.4 and 1.2.3.5 ip addr add 1.2.3.5/16 dev eth0 ip addr add 1.2.3.4/8 dev lo Question 1) (admin oriented) Is that ip addr setting sufficient? (Will set up firewall.) (The relevant post-setting output of ifconfig and ip addr are below.) Question 2) What should the settings be in main.cf for: inet_interfaces (currently "all") smtp_bind_address (unset: 1.2.3.5??, 172.17.69.230??) (Tried both.) mynetworks (unset: 172.17.69.230/16, 1.2.3.5/16, 1.2.3.4/8 ??) Question 3 & 4) Could this re-routing cause the connection to the relay server to time out? Does it affect the arguments to, or behaviour of, (postfix's) sendmail? Thanks, Dave Network settings: $ uname -a Linux P1234567 2.6.37_PQube_Bob+ #152 PREEMPT Thu Jan 16 14:47:05 PST 2014 armv5tejl GNU/Linux $ ip addr 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo inet 1.2.3.4/8 scope global lo 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000 link/ether xx:yy:zz:11:22:33 brd ff:ff:ff:ff:ff:ff inet 172.17.69.230/16 brd 172.17.255.255 scope global eth0 inet 1.2.3.5/16 scope global eth0 $ ifconfig eth0 Link encap:Ethernet HWaddr 56:CE:EC:23:65:10 inet addr:172.17.69.230 Bcast:172.17.255.255 Mask:255.255.0.0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 ... lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 UP LOOPBACK RUNNING MTU:16436 Metric:1 ...