Randomly when Sending Emails with BCC Myself Enabled Messages are Scrambled

If the BCC Myself option is enabled on some iPhones the message is received with Base64 Encoding enabled with the following header.

Content-Type: text/plain;charset="utf-8"

Content-Transfer-Encoding: base64

Some people have resolved this issue by uninstaling and reinstalling the mail app but for others the issue remains.

I've seen this reported on older iOS versions, but not iOS16.