I am running a private postfix server for my domain
mydomain.com, on server
188.8.131.52 (IP and domain sanitized for privacy reasons)
I have sent an email to
firstname.lastname@example.org which is on server
184.108.40.206. The message was deferred, and in my postfix logs, I could see following error:
postfix/smtp 9D055EA: host mail1.example.com[220.127.116.11] said: 451-18.104.22.168 is not yet authorized to deliver mail from 451 <email@example.com> to <firstname.lastname@example.org>. Please try later. (in reply to RCPT TO command)
My domain has reverse DNS record set up, and I am using SPF record. Both are configured correctly, I can send emails all right, this is the first case when I have seen these errors.
This leads me to believe, that this error is caused by misconfiguration on the destination server. But since I am not sure what these errors mean, I would like if somebody could explain it.