Hi David, we believe this problem has been cleared. If you're still having problems please update your community profile to include your full name, landline and mobile number, so that I can pass your details over to the Networks team.
To add your details you click on MY SETTINGS above the thread in blue then choose PERSONAL INFORMATION after adding your details add the email address/es in the private section and click save changes at the bottom of the page.
It will also really help if you can include a couple of the BT addresses that you can't send to and the times and dates of the failed messages.