One of our users reported a rejected email with the error code and message

Remote-MTA: dns; artemis.gat.com
Diagnostic-Code: smtp; 550 Sender IP reverse lookup rejected

We handle several domains with different outgoing smtp settings at 
multiple mail gateways:

# /etc/postfix/master.cf
wignersmtp       unix  -       -       y       -       -       smtp
        -o smtp_bind_address=
        -o smtp_bind_address6=2001:738:5001::56
        -o smtp_helo_name=smtp.wigner.mta.hu
        -o syslog_name=postfix-wigner-smtp

# /etc/postfix/main.cf
default_transport = kfkismtp
sender_dependent_default_transport_maps =

# /etc/postfix/sender_transport
@wigner.mta.hu          wignersmtp:

The sender address was from the @wigner.mta.hu domain and the IPv4/IPv6 
addresses resolve to smtp.wigner.mta.hu. The HELO name is also explicitly 
set to this name. Using debug_peer_list I could verify that the wignersmtp 
transport setting is used for @wigner.mta.hu senders indeed.

So, what kind of incorrect setting can the "Sender IP reverse lookup 
rejected" error message be mean?

Best regards,
E-mail  : kad...@blackhole.kfki.hu, kadlecsik.joz...@wigner.mta.hu
PGP key : http://www.kfki.hu/~kadlec/pgp_public_key.txt
Address : Wigner Research Centre for Physics, Hungarian Academy of Sciences
          H-1525 Budapest 114, POB. 49, Hungary

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