We solved this problem by enabling postscreen on port 26, and forwarding port 25 on the ELB to port 26 on the instance, with Proxy Protocol enabled.
This allows our local clients to connect as normal via port 25 direct to the instance, and remote incoming mail to be processed by postscreen. -- View this message in context: http://postfix.1071664.n5.nabble.com/postscreen-upstream-proxy-protocol-with-both-proxied-and-unproxied-clients-tp84489p92062.html Sent from the Postfix Users mailing list archive at Nabble.com.