Very much off topic but I run a few websites for companies and I get warning emails about various situations so that I can keep an eye on things. I noticed that over the past few days nothing had come in which was unusual. Then one of my clients said that they had received a batch of rejected email to me as follows
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A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:

xxxxxxxx@btinternet.com
host mx.bt.lon5.cpcloud.co.uk [65.20.0.49]
SMTP error from remote mail server after pipelined MAIL FROM:<office> SIZE=2333:
550 Message rejected for policy reasons (1.1.1.4) - Please check you have authority to send email from 85.233.160.25 on behalf of the domain zzzzzz.com. Guide for bulk senders www.bt.com/bulksender
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Basically my hosting company's email system can't send to my btinternet.com email account. I googled the problem and lots of BT people are experiencing it so has anyone on the forum come across this? 3 x FL1 2 manual + 1 auto
5 x FL2 4 manual + 1 auto
Now Discovery Sport P250 MHEV SE

Potentially, BT is viewing these as spam and bouncing them due to policy reasons, which generally means spam.

Who are the emails coming from? Do you have reverse DNS lookup records for your domain and IP address of the sender? Many receiving mail servers will check to see if the domain the email is apparently from really is from it and if it isn't, it'll bounce.

If it used to work and now it doesn't, either your domain host may have changed something or BT has. You'd be better served asking your host for advice before you even think about speaking to BT.

Hope that's of some help. Learned to drive in 2011.
Bought a Micra - great little car
"Upgraded" to Kia Sportage - hated it
Proper upgrade to FL2 TD4 GS 60 reg Facelift - tailgate paint issues, fuel gauge rewire, transfer box failure at 36k miles, clutch at 60k
Reconditioned diff at 70k ish
Sold at 84k and now on a DS. Terribly unreliable.
Sold DS for a 2021 Mitsubishi Outlander PHEV. Fingers crossed....
Sold Outlander for a 2014 SD4 SE Tech because I’m mental

The annoying thing is that the emails are genuine ones created by my website and then rejected by BT. I have just had an email from my domain host and they are aware of the problem, advice is to forward stuff to a non BT email address until it gets sorted! 3 x FL1 2 manual + 1 auto
5 x FL2 4 manual + 1 auto
Now Discovery Sport P250 MHEV SE

Oh yes, they can be genuine but if not 100% correctly configured some more strict mail servers may reject them. BT have likely made a change somewhere that has caused this problem. They will no doubt, at some point, fix it. You'll just have to test it every now and again. Or set up an alternative one that makes it very clear it was sent to the BT address so you know when it starts working again. Learned to drive in 2011.
Bought a Micra - great little car
"Upgraded" to Kia Sportage - hated it
Proper upgrade to FL2 TD4 GS 60 reg Facelift - tailgate paint issues, fuel gauge rewire, transfer box failure at 36k miles, clutch at 60k
Reconditioned diff at 70k ish
Sold at 84k and now on a DS. Terribly unreliable.
Sold DS for a 2021 Mitsubishi Outlander PHEV. Fingers crossed....
Sold Outlander for a 2014 SD4 SE Tech because I’m mental

I had this too. BT are blocking emails sent from a domain without an SPF record. My host told me how to add this to my domain's DNS and all is now working.

So when did this start? 3 x FL1 2 manual + 1 auto
5 x FL2 4 manual + 1 auto
Now Discovery Sport P250 MHEV SE

I first noticed it on the 18th January. My hosting company were aware of it and luckily I stumbled over their support page notification after 3 or 4 days of bounced e-mails to one of my clients.

Would have been nice if my host had sent out an e-mail to all of their customers who didn't have an SPF record to let us know we needed to add one.