We're having the same problem.
Customers are registering on our website for event tickets and customers with BT emails aren't getting their tickets.
No issues with other ISPs.
Email routed over Amazon SES.
Another one with the same problem;
Reason: 554 Message rejected on 2019/10/18 18:14:04 BST, policy (188.8.131.52) ID (5D6F956C08A4B976) - Your message looks like SPAM or has been reported as SPAM
Initially I went to https://www.cyren.com/security-center/cyren-ip-reputation-check
to make sure all was well but I'm not sure if this company looks after the Email filters for BT anymore.
I tried logging a call through BT but they couldn't help so came here. I have sent an email to firstname.lastname@example.org today to see if they can expedite matters.
Us too. Our membership list on mailman. Btinternet is rejecting emails from our own mailing list on our own VPS to our own members. Note the bit about "Our Postmaster will be unable to help you". Well thanks bt.
SMTP error from remote mail server after end of data: 421-Policy () Too much SPAM received from [our ip address] on [date]. As we detected too much spam, we protected our customers by not allowing any more emails from this IP\n421 till we notice an improvement. You may have been affected unknowingly through your email provider. Please contact your email provider to assist. Our Postmaster will be unable to help you.