I received this email after contacting BT about ALL of my sent emails being deleted. I contacted 2 days after they deleted all of my emails, and they are still claiming data recovery is not possible. This is a disgusting response from BT. No attempt to tell me which supposed setting caused them all to be deleted, no assurance that this is a bug they're conscious of and are actively resolving. AND if this is 'a fairly common issue', why in the world do they not have a back up to ensure clients' data can be recovered. I am so unbelievably offended by this response.
If the problem is with the Apple mail app I'm not sure why you think BT would be trying to resolve it.
However, I am surprised the mails have been permanently deleted from the server and are not recoverable.
Conversely, if it were a BT problem, it wouldn't just be happening on Apple Mail, it would also affect Android apps. The mail servers won't be aware of what app is being used.