Re: An observation - it is possible the passwords have been cracked
"The more I puzzled over this, the more it looked like it was basically listing the history of messages sent from my Yahoo! account."
Had something like that happen with two old Yahoo accounts too - spam sent to contacts in my history. Fortunately I mostly used those to mail myself rather than others. When I checked the connection log in Yahoo it showed that the accounts had been accessed by some app, quite a while before the spam. The odd thing is, Yahoo normally warns you when the account is accessed from a new device or region, but didn't raise a warning in this case.
Biting the hand that feeds IT
