Emails Rejected by Plusnet (John Lewis) Server as spam

[#1]

Morning all. 

I have my own domain name and I am sending emails to a Plusnet account and the emails are rejected for spam. I happen to be a Plusnet user too. The details are below.

I can't find an email address to send the details to so it can be taken off the spam list.

Can anyone help.

Thanks:)

Philip

From: MAILER-DAEMON@mailchannels.net (Mail Delivery System)
Date: 8 August 2019 at 20:51:58 BST
To: *************
Subject: Undelivered Mail Returned to Sender

This is the mail system at host relay.mailchannels.net.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

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

<*********@john-lewis.com>: host mx.avasin.plus.net[212.159.9.200] said: 552 Spam
   Message Rejected  (in reply to end of DATA command)

Reporting-MTA: dns; relay.mailchannels.net
X-Postfix-Queue-ID: D4C3514242C
X-Postfix-Sender: rfc822; *****************
Arrival-Date: Thu,  8 Aug 2019 19:51:46 +0000 (UTC)

Final-Recipient: rfc822; ********@john-lewis.com
Original-Recipient: rfc822;*********@john-lewis.com
Action: failed
Status: 5.0.0
Remote-MTA: dns; mx.avasin.plus.net
Diagnostic-Code: smtp; 552 Spam Message Rejected

[#2]

Probably the wrong place to post this so I have copied to email forum.