Subject: Delayed Mail (still being retried)
From: Mail Delivery System <[email-masked]>
To: [email-masked]
Date: Sat, 9 Dec 2023 20:30:50 +0100 (CET)

This is the mail system at host mailout.example.com.

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# THIS IS A WARNING ONLY.  YOU DO NOT NEED TO RESEND YOUR MESSAGE. #
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Your message could not be delivered for more than 0 hour(s).
It will be retried until it is 5 day(s) old.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

<[email-masked]>: host cdxmailin01.blah.blubb[fd00:e50:f155:7::d0] said:
    450 4.2.0 <[email-masked]>: Recipient address rejected: Sorry,
    please retry later. see
    https://postmaster.blah.blubb/greylisting/hilfe/blah.blubb.html, servertime=Dec
    09 20:30:50, server=mailin.prod.blah.blubb, client=fd03:4000:21:81b::1 (in
    reply to RCPT TO command)