Yeah, I've just seen that the London visa does not have an email address for any communication.I also got reply previously from this email.when i used CSE and CSE now showing me sending failed.
i got reply from this email address as it says
Your enquiry has been received by the London visa office. We respond to all enquiries within 28 days. Enquiries marked as urgent by the sender and deemed urgent after review will receive a response within 24 to 48 hours. Film/Media crews travelling on short notice will receive a response within 5 days. If you have submitted new information, we will update your file without replying to confirm.
The CSE exists and you've sent it correctly