This started happening a couple of years ago. Yahoo could not trace the sender, but they assured me that my email was not hacked. They are apparently sending emails from a totally different address, but are using my personal email address in the line as the apparent sender. Hell I get spam from myself too.
Gary,
I forwarded the first email back to you via a website email address and sending to your Yahoo account.
Then received an immediate reply from the 'hacker' to the 2d email address with a different URL.
Despite what Yahoo says (they are full of shit), your account is hacked, else the hacker wouldn't have the capability to view the emails when they arrive so quickly.
I've both saved emails. The headers are different, however it makes no sense at all to send them to a Yahoo account that is hacked (or at least privy) for another to view.