The closest thread I could find for this is almost 10 years old: http://postfix.1071664.n5.nabble.com/Customize-configure-postfix-with-multiple-recipients-td45030.html#a45035From that thread, my Postfix is somehow not handling the email properly as the rejection done early on seems to result in setting the From to null / <> for all other emails.I could reproduce every time I am sending an email to a list of contacts containing 1 invalid address (bad domain).Main email providers respond differently to it: - Googlemail blocks it and shouts that "this message is not RFC 5322 compliant." - Microsoft accepts the email but it's empty.From the logs I see that the From header has been removed even before it reached the opendkim / opendmarc milters.*If I send the same email to all valid recipients, all is well.*Here are the logs after sanitizing (hopefully still readable):Jul 23 09:44:35 myhost postfix/smtpd[26369]: connect from XXX.XXX.XXX.137.threembb.co.uk[XXX.XXX.XXX.137]Jul 23 09:44:35 myhost postfix/smtpd[26369]: Anonymous TLS connection established from XXX.XXX.XXX.137.threembb.co.uk[XXX.XXX.XXX.137]: TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)Jul 23 09:44:35 myhost postfix/smtpd[26369]: CEC231003: client=XXX.XXX.XXX.137.threembb.co.uk[XXX.XXX.XXX.137], sasl_method=PLAIN, sasl_username=obsucated-p@domain.frJul 23 09:44:35 myhost postfix/smtpd[26369]: CEC231003: reject: RCPT from XXX.XXX.XXX.137.threembb.co.uk[XXX.XXX.XXX.137]: 450 4.1.2 <obsucate...@domain.com>: *Recipient address rejected: Domain not found*; from=<obsucate...@domain.fr> to=<obsucate...@domain.com> proto=ESMTP helo=<[XXX.XXX.XXX.119]>Jul 23 09:44:36 myhost postfix/cleanup[26374]: CEC231003: message-id=<>Jul 23 09:44:36 myhost opendkim[32642]: *CEC231003: can't determine message sender; accepting*Jul 23 09:44:36 myhost opendmarc[619]: CEC231003: RFC5322 requirement error: missing From field; acceptingJul 23 09:44:36 myhost postfix/qmgr[26269]: CEC231003: from=<obsucate...@domain.fr>, size=213, nrcpt=2 (queue active)Jul 23 09:44:36 myhost postfix/smtp[26375]: Untrusted TLS connection established to gmail-smtp-in.l.google.com[2a00:1450:400c:c0a::1b]:25: TLSv1.2 with cipher ECDHE-RSA-CHACHA20-POLY1305 (256/256 bits)Jul 23 09:44:36 myhost postfix/smtpd[26369]: disconnect from XXX.XXX.XXX.137.threembb.co.uk[XXX.XXX.XXX.137] ehlo=2 starttls=1 auth=1 mail=1 rcpt=2/3 data=1 quit=1 commands=9/10Jul 23 09:44:36 myhost postfix/smtp[26375]: CEC231003: to=<obsucate...@domain.com>, relay=gmail-smtp-in.l.google.com[2a00:1450:400c:c0a::1b]:25, delay=0.99, delays=0.4/0.01/0.16/0.43, dsn=5.7.1, status=bounced (host gmail-smtp-in.l.google.com[2a00:1450:400c:c0a::1b] said: 550-5.7.1 [2a01:4f8:10a:2493:b827:a8ff:fe4b:b71c 11] Our system has 550-5.7.1 detected that this message is not RFC 5322 compliant: 550-5.7.1 'From' header is missing. 550-5.7.1 To reduce the amount of spam sent to Gmail, this message has been 550-5.7.1 blocked. Please visit 550-5.7.1 https://support.google.com/mail/?p=RfcMessageNonCompliant 550 5.7.1 and review RFC 5322 specifications for more information. y4si40902182wrr.356 - gsmtp (in reply to end of DATA command))Jul 23 09:44:36 myhost postfix/smtp[26375]: CEC231003: to=<obsucate...@domain.com>, relay=gmail-smtp-in.l.google.com[2a00:1450:400c:c0a::1b]:25, delay=0.99, delays=0.4/0.01/0.16/0.43, dsn=5.7.1, status=bounced (host gmail-smtp-in.l.google.com[2a00:1450:400c:c0a::1b] said: 550-5.7.1 [2a01:4f8:10a:2493:b827:a8ff:fe4b:b71c 11] Our system has 550-5.7.1 detected that this message is not RFC 5322 compliant: 550-5.7.1 'From' header is missing. 550-5.7.1 To reduce the amount of spam sent to Gmail, this message has been 550-5.7.1 blocked. Please visit 550-5.7.1 https://support.google.com/mail/?p=RfcMessageNonCompliant 550 5.7.1 and review RFC 5322 specifications for more information. y4si40902182wrr.356 - gsmtp (in reply to end of DATA command))Jul 23 09:44:36 myhost postfix/cleanup[26374]: CAA341B99: message-id=<20190723084436.caa341bobsucate...@domain.fr>Jul 23 09:44:36 myhost postfix/qmgr[26269]: CAA341B99: from=<>, size=4503, nrcpt=1 (queue active)Jul 23 09:44:36 myhost postfix/bounce[26376]: CEC231003: sender non-delivery notification: CAA341B99Jul 23 09:44:36 myhost postfix/qmgr[26269]: CEC231003: removedJul 23 09:44:37 myhost postfix/pipe[26377]: CAA341B99: to=<obsucate...@domain.fr>, relay=dovecot, delay=0.24, delays=0.12/0/0/0.12, dsn=2.0.0, status=sent (delivered via dovecot service)Jul 23 09:44:37 myhost postfix/qmgr[26269]: CAA341B99: removed
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