Sep 09 10:06:58 mail.private43.com postfix/smtp[361594]: C37B21408EF: to=, orig_to=, relay=mailserver.example.org[xxx.xx.xxx.xx]:25, delay=6.8, delays=0.04/0.01/2.7/4, dsn=5.7.1, status=bounced (host mailserver.example.org[xxx.xx.xxx.xx] said: 554 5.7.1 This message does not meet our delivery requirements (in reply to end of DATA command)) Sep 09 10:06:58 mail.private43.com postfix/cleanup[361593]: AABA3140901: message-id=<20260909080658.AABA3140901@privatemailexample.com> Sep 09 10:06:58 mail.private43.com postfix/qmgr[322346]: AABA3140901: from=<>, size=7080, nrcpt=1 (queue active) Sep 09 10:06:58 mail.private43.com postfix/bounce[361601]: C37B21408EF: sender non-delivery notification: AABA3140901 Sep 09 10:06:58 mail.private43.com postfix/qmgr[322346]: C37B21408EF: removed Sep 09 10:06:59 mail.private43.com postfix/smtp[361598]: AABA3140901: to=, relay=gmail-smtp-in.l.google.com[142.251.182.27]:25, delay=0.62, delays=0.04/0/0.18/0.39, dsn=5.7.26, status=bounced (host gmail-smtp-in.l.google.com[142.251.182.27] said: 550-5.7.26 Your email has been blocked because the sender is unauthenticated. 550-5.7.26 Gmail requires all senders to authenticate with either SPF or DKIM. 550-5.7.26 550-5.7.26 Authentication results: 550-5.7.26 DKIM = did not pass 550-5.7.26 SPF [] with ip: [xxx.xx.xxx.xx] = did not pass 550-5.7.26 550-5.7.26 For instructions on setting up authentication, go to 550 5.7.26 https://support.google.com/mail/answer/81126#authentication 6a1803df08f44-9104072e7a1si221877546d6.79 - gsmtp (in reply to end of DATA command))