Looks like you are using Google's SMTP servers to send a email from the domain btinternet.com/btopenword.com. There is a policy in place to reject/bounce back all emails that are not sent from a valid smtp server.
This is why your email is being rejected.
You need to use the dedicated smtp servers for a @email@example.com domain http://bt.custhelp.com/app/answers/detail/a_id/44917/~/what-are-the-settings-for-outgoing-and-incomi...
Ive been trying to contact my local council but i keep getting a delivery failed error message, saying that btopenworld is not accepted. I dont quite understand what the message means and why it isnt delivering my message. I will paste the error message below - id be very grateful if someone could interpret this error message please.
How have you set up your email address to send emails? What app/client are you using?
Has this just started to happen?
which should enable you to send your btinteret/btopenworld emails using gmail servers.