bind postfix to the right network interface when sending outbound mail so that...

bind postfix to the right network interface when sending outbound mail so that SPF checks on the receiving end will pass

fixes #3 (again)

CHANGELOG.md

@@ -5,6 +5,7 @@ In Development
 --------------
 
 * Roundcube updated to version 1.1.4.
+* On multi-homed machines, Postfix now binds to the right network interface when sending outbound mail so that SPF checks on the receiving end will pass.
 
 v0.16 (January 30, 2016)
 ------------------------

setup/mail-postfix.sh

@@ -57,11 +57,14 @@ apt_install postfix postfix-pcre postgrey ca-certificates
 # Set some basic settings...
 #
 # * Have postfix listen on all network interfaces.
+# * Make outgoing connections on a particular interface (if multihomed) so that SPF passes on the receiving side.
 # * Set our name (the Debian default seems to be "localhost" but make it our hostname).
 # * Set the name of the local machine to localhost, which means xxx@localhost is delivered locally, although we don't use it.
 # * Set the SMTP banner (which must have the hostname first, then anything).
 tools/editconf.py /etc/postfix/main.cf \
 	inet_interfaces=all \
+	smtp_bind_address=$PRIVATE_IP \
+	smtp_bind_address6=$PRIVATE_IPV6 \
 	myhostname=$PRIMARY_HOSTNAME\
 	smtpd_banner="\$myhostname ESMTP Hi, I'm a Mail-in-a-Box (Ubuntu/Postfix; see https://mailinabox.email/)" \
 	mydestination=localhost