Legitimate emails to btinternet.com rejected as spam (policy 3.2.1.1)

[Nordur]

Hello,

I handle email for a small UK expedition business (domain nordur.co.uk) and send low-volume, one-to-one transactional messages to clients via Google Workspace. Mail to a customer on btinternet.com is being rejected as spam, on both a test send and the live send. The two bounces were:

554 Message rejected on 2026/05/30 18:00:18 BST, policy (3.2.1.1) ID (69F6353B0962BB9D)
554 Message rejected on 2026/05/30 17:52:00 BST, policy (3.2.1.1) ID (69F64AB9095A77D9)

SPF, DKIM and DMARC all pass for nordur.co.uk (confirmed via Gmail's Show original: dkim=pass, spf=pass, dmarc=pass). This is genuine mail the customer is expecting, not bulk or marketing. The sending domain is fairly new, so I suspect a content or reputation score rather than a blocklist entry.

Could you help me understand why it is being scored as spam, and get the sender delisted if needed? I am happy to provide the recipient's address and full message headers by private message.

Thanks,
Steve
Nordur Expeditions

[licquorice]

This is a customer to customer self help forum.

You need to email the BT postmaster at postmaster@btinternet.com

[Nordur]

Thanks. Already done - confirmed delivered to BT's mail server via Google Workspace logs, so will give it 48 hours before chasing.

If a BT moderator picks this up in the meantime, happy to share details by PM.

Will report back once I hear back, in case it helps anyone else hitting 3.2.1.1.