Because friends with BTinternet.com addresses feel that they cannot change. As my email address is hosted as part of my web hosting package with justhost.com would not the problem remain the same?
Of course not, you wouldn't be using BT mail servers you would still be using your hosting company's mail servers as now. It is not compulsory to have an @btinternet.com email address.
Thank you. However, the problem of sending to btinternet.com addresses and getting a clear and straightforward solution to the problem remains.
@Simon-D - I can assure that its nothing to do with the subject or email content as we've tested it with the email content stripped down to just a couple of words and it still bounces. We've also worked through all the advice at www.bt.com/bulksender. We have also sent a number of emails to the firstname.lastname@example.org account but we've had no replies. What do you suggest next?
In my experience this has nothing to do with your emails or their content but the reputation of your mail hosting company. If they have allowed some dubious spammer to send from their email server then it’s all the domains hosted on that IP address that get blocked. Of course if you are using your own server then that’s a different matter.
Don't even think about it on a dynamic IP from an ISP residential service.
I have a fixed IP...
So if you moved ISP to BT Business, with a fixed IP address, you would be given .btconnect.com which has nothing to do with the residential email service, and instead uses Office365.
With regard to your original problem, are you sure your hosting company has configured your SPF/DKIM/DMARC credentials correctly?