Holy crap - this happened to me a couple days ago. I am glad it wasn't from something I did. I salvaged my contacts from the sent email that was SPAM in the first place, then I got a new email address from Google. I've had the same email address with yahoo for 6 years with no problem, now...I also have a MAC and have never had issues like this before.
I emailed yahoo on Saturday when I noticed the wacky email. I got a response today, saying that they got my email. That's it.
This is HUGE and I can't believe that yahoo has not sent anything out to all the yahoo email subscribers, either alerting or explaining the issue to them.
Life is what happens to you while you're busy making other plans.
John Lennon, "Beautiful Boy"