Got it work. Finally. It seems the fact it was attempting to run in compatibility mode screwed everything up. So I:
. Started a main.cf from scratch from the main.cf.default . ran postconf compatibility_level=2 Voilà. This worked for me. I'm able to relay to Gmail again: command_directory = /usr/sbin compatibility_level = 2 daemon_directory = /usr/libexec/postfix data_directory = /var/lib/postfix debug_peer_level = 2 debugger_command = PATH=/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin ddd $daemon_directory/$process_name $process_id & sleep 5 html_directory = no inet_protocols = ipv4 mail_owner = _postfix mailq_path = /usr/bin/mailq manpage_directory = /usr/share/man newaliases_path = /usr/bin/newaliases queue_directory = /var/spool/postfix readme_directory = /usr/share/doc/postfix relayhost = smtp.gmail.com:587 sendmail_path = /usr/sbin/sendmail setgid_group = _postdrop smtp_sasl_auth_enable = yes smtp_sasl_mechanism_filter = plain smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd smtp_sasl_security_options = noanonymous smtp_tls_security_level = encrypt smtp_use_tls = yes tls_random_source = dev:/dev/urandom unknown_local_recipient_reject_code = 550 -- Sent from: http://postfix.1071664.n5.nabble.com/Postfix-Users-f2.html
