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I am running a private postfix server for my domain mydomain.com, on server (IP and domain sanitized for privacy reasons)

I have sent an email to info@example.com which is on server The message was deferred, and in my postfix logs, I could see following error:

postfix/smtp  9D055EA: host mail1.example.com[] said: 
451- is not yet authorized to deliver mail from 451 
<martin@mydomain.com> to <info@example.com>. 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.

share|improve this question
Does the destination server have greylisting enabled? –  Greg Hewgill Jul 17 at 23:10
@Greg Hewgill - I don't know. The destination server is not under my control. –  Martin Vegter Jul 18 at 10:38
Did the retry succeed after sometime? –  clement Jul 20 at 10:57
@clement - I did not wait to see if it would have succeeded. I have removed the mail from queue and sent it from gmail instead. –  Martin Vegter Jul 21 at 6:01

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