Onze mail server door KPN blacklisted?

> From: MAILER-DAEMON@juliushost.org
> Date: 3 June 2022 at 00:24:13 CEST
> To: xx@@xx
> Subject: Delayed Mail (still being retried)
> 
> This is the mail system at host juliushost.org.
> 
> ####################################################################
> # THIS IS A WARNING ONLY.  YOU DO NOT NEED TO RESEND YOUR MESSAGE. #
> ####################################################################
> 
> Your message could not be delivered for more than 1 hour(s).
> It will be retried until it is 14 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
> 
> <xx@@telfort.nl>: host mx.kpnmail.nl[195.121.65.158] refused to talk
>    to me: 521 5.5.0 Your IP has been blacklisted. Please contact abuse@kpn.com
>    for more information.
> Return-Path: Received: from localhost (localhost [127.0.0.1]) by
juliushost.org (Postfix) with ESMTP id 79DDA209D67; Thu, 2 Jun 2022 23:21:44
+0200 (CEST) Authentication-Results: juliushost.org (amavisd-new); dkim=pass
(4096-bit key) reason="pass (just generated, assumed good)"
header.d=xx@xxx DKIM-Signature: v=1; a=rsa-sha256;
c=relaxed/simple; d=xx@xxx;
h=content-transfer-encoding:content-type:content-type
:in-reply-to:from:from:references:content-language:subject
:subject:user-agent:mime-version:date:date:message-id; s= default;
t=1654204904; x=1656019305; bh=3XDiAqkQHwYDwQ/udkZCK0Oc
zgOYhCXJJozIZTOVrOo=; b=KVgR9bR6whIm9YdbNelcZvBXmORjf96uejTkhRP8
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XFd+1wnvyclt/PikHEtWXLWKORJ1o9qy3fBLMysMqRnxB6jc6Wx/iIeUZ5VpT0eM qB8=
Received: from juliushost.org ([127.0.0.1]) by localhost (juliushost.org
[127.0.0.1]) (amavisd-new, port 10026) with ESMTP id hE_73L6eZWRz; Thu, 2
Jun 2022 23:21:44 +0200 (CEST) Received: from [192.168.1.74] (unknown
[89.205.129.255]) (Authenticated sender: xx@@xx) by
juliushost.org (Postfix) with ESMTPSA id 4F873209D66; Thu, 2 Jun 2022
23:21:43 +0200 (CEST) Message-ID:
<696fe4a9-ea0d-66bf-3f15-fa637ce9cf5c@xx@xxx> Date: Thu, 2 Jun 2022
23:21:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel
Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 Subject: Re: xxxx
Content-Language: nl
To: xx@xx
Content-Transfer-Encoding: 7bit

(namen en adressen gemaskeerd met xx)
Vreemd genoeg zie ik geen enkele keer het IP van onze mail-server listed in the responses van de kpn server (voor mail aan @telfort.nl adres dus). Als ik zoek op https://blacklist.kpnmail.nl/ krijg ik ook niets over een blacklisting van ons server IP.

Kunt u in uw logs kijken wat hier loos is? En dan met name op basis van tijdstip en code van Message-ID vóór het @ teken;

Message-ID:<696fe4a9-ea0d-66bf-3f15-fa637ce9cf5c@xx> Date: Thu, 2 Jun 202223:21:41 +0200

Mail van onze mailserver is voorheen nooit geblokkeerd geweest door KPN, vandaar.

J