Thanks for all the replies. Yes, DNS is working as expected. I can resolve the relay host's address no problem.
There is a firewall between them. Traffic is open between both sides. My postfix server is running on 25587/tcp and the relay hosts are both listening on the same. I can successfully telnet into both relay hosts boxes individually, as well as through the load-balanced address. I am not hosting this on a fileserver. Hosting on an Ubuntu VM with local storage. All postfix servers have their times set up correctly though. Here's a pastebin of postfinger: https://pastebin.com/t8wa3kjH Here's a pastebin of my postconf -n: https://pastebin.com/x7vQkjMP Here's a copy of a problematic message's log: May 21 15:14:43 mail postfix/pickup[13108]: 3AA2E3F9AD: uid=0 from=<r...@domain.com> May 21 15:14:43 mail postfix/cleanup[13125]: 3AA2E3F9AD: message-id=<20180521151443.3aa2e3f...@domain.com> May 21 15:14:43 mail postfix/qmgr[13109]: 3AA2E3F9AD: from=<r...@domain.com>, size=338, nrcpt=1 (queue active) May 21 15:19:44 mail postfix/smtp[13170]: 3AA2E3F9AD: conversation with load-balanced-dns-name[10.55.128.92] timed out while receiving the initial server greeting May 21 15:19:44 mail postfix/smtp[13170]: 3AA2E3F9AD: to=<m...@differentdomain.com>, relay=internal-load-balancer[10.55.128.125]:25587, delay=301, delays=0.01/0.02/301/0.11, dsn=2.0.0, status=sent (250 2.0.0 Ok: queued as 6A10E61A76) May 21 15:19:44 mail postfix/qmgr[13109]: 3AA2E3F9AD: removed I do see the "conversation with load-balanced-dns-name[10.55.128.92] timed out while receiving the initial server greeting" message now, but I don't know where to look here. I can successfully hit both servers behind the load balanced endpoint, as well as telnet into the correct port I've set up (25587/tcp). The message attempts the first time, fails, then succeeds the second time -- every time. I did attempt to change tcp_window_scaling to "0" in sysctl (found on another forum), but this unfortunately did not do the trick for me (net.ipv4.tcp_window_scaling = 0 for reference). Just to be completely transparent on how my setup is here, mail is flowing as follows: mail -> postfix -> openVPN connection -> load balancer -> relay host 1 and 2 Traffic is flowing between this connection stream. Thank you. -- Sent from: http://postfix.1071664.n5.nabble.com/Postfix-Users-f2.html
