Postfix error: not yet authorized to deliver mail

Question

I am running a private postfix server for my domain mydomain.com, on server 111.111.111.111 (IP and domain sanitized for privacy reasons)

I have sent an email to [email protected] which is on server 222.222.222.222. The message was deferred, and in my postfix logs, I could see following error:

postfix/smtp  9D055EA: host mail1.example.com[222.222.222.222] said: 
451-111.111.111.111 is not yet authorized to deliver mail from 451 
<[email protected]> to <[email protected]>. 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.

Answer 1

The message "... is not yet authorized to deliver mail from ..." is similar to a greylist implementation described in Adding Greylisting Support. If the destination server implement similar script, you can send your mail by flushing your queue to retry sending soon.

$ postqueue -f

The greylist implementation works as follows;

1. If a mail come from an unauthorized host, the server replies 451 and save a entry including sender/recipient/IP/...
2. When the host retry to send the mail, the server checks whether all sender/recipient/IP are matched. If matched, the server accept the mail.

I think this idea is come from most spammer implementation. It sends many mails to random recipient with random sender addresses. So it never send to the same recipient.