BT and 554 Message rejected for policy reasons (3.2.2.1)

BT or British Telecom are the largest broadband supplier in the UK providing connections to consumers and businesses. Currently any mailpoet sourced message sent to any one of several BT addresses (btinternet.com, btopenworld.com etc) are receiving a rejection message. In one database of 900 UK subscribers, 186 are from BT all of them send the same bounce back message. All of the other email addresses continue to work ok. The sending service is not blacklisted, does not have a poor reputation, DMARC, SPF and DKIM are correctly configured. Rate sending is set at 100 emails an hour (where the limit is 250/hr). This system has worked fine until recently. BT has introduced something which is preventing them from being sent. I was on a support call for 1hr 40 mins yesterday with BT where I demonstrated the problem to them. They have concluded that as I can send other mail to and from a BT account and only this newsletter is being blocked that the BT service is working correctly. They cannot tell me what is being triggered, or what the message or policy: 554 Message rejected for policy reasons (3.2.2.1) means.

Apart from closely examining both ends of the system, I have found the following out:
1) A newsletter sent out (just one) to a btinternet.com user does not get through.
2) A newsletter is sent to subscriber X. Subscriber X Forwards the newsletter to a btinternet.com account. It does not get through.
3). A newsletter is sent to subscriber X. Subscriber X removes the top part of the newsletter which contains some automated information created by the MailPoet App it does get through.

I assume there is some sort of filtering going on here, but cannot see precisely what it is. Is this something you can help with? I do not believe it is anything to do with being on a spam list otherwise mail would never reach the btinternet.com account. BT are absolutely useless indicating “we do not have access to that information” so right now my only option is to go to the government ombudsmen that controls telecommunications in the UK (OfCom) and make a formal complaint. BT is too large a service provider to ignore as this affects many people.

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