I assume it's .eml - this is a pretty simple and obvious text format based on SMTP and email headers. And it has been around since at least 1982[1] [1] https:/

I assume it's .eml - this is a pretty simple and obvious text format based on SMTP and email headers. And it has been around since at least 1982[1] [1] https://datatracker.ietf.org/doc/html/rfc822 https://datatracker.ietf.org/doc/html/rfc822