[lists.typo3.org] IPv6 delivery to Google Mail
Jul 20 12:20:35 srv102 postfix/smtp[30252]: 6D074EC2F45: to=<XXX@gmail.com>, relay=gmail-smtp-in.l.google.com[2a00:1450:400c:c0c::1a]:25, delay=29, delays=0.18/16/0.06/13, dsn=5.7.1, status=bounced (host gmail-smtp-in.l.google.com[2a00:1450:400c:c0c::1a] said: 550-5.7.1 [2a01:198:1:1::102] Our system has detected that this message does not 550-5.7.1 meet IPv6 sending guidelines regarding PTR records and authentication 550-5.7.1 . Please review 550-5.7.1 https://support.google.com/mail/?p=IPv6AuthError for more information 550 5.7.1 . o17si1787364wrh.388 - gsmtp (in reply to end of DATA command))
Maybe disable IPv6 on the legacy listserver altogether?