• There is many malware that scans for passwords/login names. Could this be the case here?

  • There is also a lot of malware that generate (speudo) random ip addresses to send itself to. Could this be the case here?

When I was looking for basic compiler I found a little basic program that was able to send email to someone and I could choose who the sender and sender server was. With that I can send you a mail that looks like you have send it to yourself. Little editing and it will generate random addresses/names and send it to all. If I let it run long enough sooner or later you too will get such a mail. Not that I run this program ofcourse. But it illustrates very well that not all things are as they appear to be.

I think the main issue here is getting your system(s?) clean and secured. At least that is what I make out of your posts.