We have received several reports of issues with BT. You may receive this error when sending messages to btinternet.com recipients.
The e-mail system was unable to deliver the message, but did not report a specific reason. Check the address and try again. If it still fails, contact your system administrator.
< outbound2.exchangedefender.com #5.0.0 SMTP; 554 <email@example.com>: Relay access denied>”
We have notified BT by e-mail and phone regarding the issue, the problem is on their end. Since this is a configuration issue on BT network we have no ETA, no resolution time or idea of what may be going wrong.
For more information about proxy errors, click here.