I have several mailboxes @btinternet.com but I am finding that numerous mailservers have blacklisted messages with the @btinternet.com domain.
I know it's not just my mailboxes being blacklisted as I have spoken to many other users who are all experiencing the same problem. Why are @btinternet.com seemingly being blocked by so many service providers?
have you asked the companies that are blocking your email why it is happening? if your email is accepted by some companies and not others then the problem is not at BT end but with the companies that are blocking them