I assume there is no answer, but reading https://postmaster.t-online.de/#t3 points towards https://en.wikipedia.org/wiki/Forward-confirmed_reverse_DNS
From /etc/postfix/main.cf on elsa (and anna):
myhostname = hydra.opensuse.org
So let's see what we get when asking for this name:
~> host hydra.opensuse.org
hydra.opensuse.org has address 195.135.221.150
hydra.opensuse.org has IPv6 address 2620:113:80c0:8::19
As result, a forward-confirmed reverse DNS check will obviously fail.
I guess, this is a history failure, when the machines were setup as copy of the original tarzan/jane proxies. (hydra.opensuse.org is the name of this pair on the external HA interface.)
The file /etc/sysconfig/postfix on both machines does not really help. The file is the same on anna and elase and contains:
POSTFIX_MYHOSTNAME="anna.opensuse.org"
POSTFIX_RELAYHOST="[relay.infra.opensuse.org]"
While it might make at least a little sense on anna, the use of a relayhost entry does not make sense if anna/elsa should be the relay hosts for the internal machines. But luckily /etc/sysconfig/mail contains:
MAIL_CREATE_CONFIG="no"
So main.cf and master.cf on anna and elsa will not get touched by /usr/sbin/config.postfix.
My suggestion: configure master.cf for the external IPs on anna/elsa. Have a look at this page for more details.
But I hope we have more Email experts around that could assist here.