Try to route outgoing messages through diff IPs depending on trust

Ideally, if there was auth on a message (kerberos/password remotely, or
legitimately sourced locally -- mailman messages dubiously count), we'd use one
IP, and forwarded messages (eg, mail to jim@ being forwarded to GMail) would
use another. That way, when GMail decided to hate the latter, the (more
important) former would still go through. I'm not quite sure how to decide
based on auth, so instead, I just whitelisting a few envelope senders, but it's
better than nothing.

See
https://serverfault.com/questions/663979/virtual-alias-domains-how-to-use-different-ip-addresses-when-forwarding-mail,
http://www.postfix.org/postconf.5.html#smtp_bind_address, and
http://www.postfix.org/postconf.5.html#sender_dependent_default_transport_maps
for some relevant docs.

diff --git a/main.cf b/main.cf
index 704122a1e47cdf53cb4ab1254c4093e5be4b9454..5c8b27727cad451e1750fd15bd4b2ba6f92fdeda 100644 (file)
--- a/main.cf
+++ b/main.cf
@@ -278,6 +278,11 @@ smtpd_use_tls = yes
 smtpd_tls_auth_only = yes
 smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
 smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
+
+# Alex Dehnert, 2017-11-01
+# Based on https://serverfault.com/questions/663979/virtual-alias-domains-how-to-use-different-ip-addresses-when-forwarding-mail
+
+sender_dependent_default_transport_maps = hash:/etc/mail/sender-transport
     
 # The relay_domains parameter restricts what destinations this system will
 # relay mail to.  See the smtpd_recipient_restrictions description in

diff --git a/master.cf b/master.cf
index a74a5f524c24b625099ea750285c362bd96b689d..e04e05c027c78a3237169a12b88a430f83af5231 100644 (file)
--- a/master.cf
+++ b/master.cf
@@ -60,6 +60,9 @@ smtp      inet  n       -       -       -        5      smtpd
         -o mynetworks=127.0.0.0/8
         -o receive_override_options=no_unknown_recipient_checks
 
+smtp-forward    unix  -  -   n       -       -       smtp -o smtp_bind_address=18.102.208.11
+smtp-local      unix  -  -   n       -       -       smtp -o smtp_bind_address=18.102.208.44
+
 # When relaying mail as backup MX, disable fallback_relay to avoid MX loops
 relay     unix  -       -       -       -       -       smtp
        -o smtp_fallback_relay=