Your email is most likely on the BCC (blind carbon copy) line of the email. Normally spammers don't bother to go to great lengths to cover the fact that they are sending a mass mailing but apparently yours is trying to hide it.
Out of respect for people's privacy, we suggest this technique if you must send out an email with several email addresses on it. You probably don't like your email put out there by other people and you should be mindful of the same thing. We suggest to keep people's email addresses private, putting your own email on the TO line whenever you need to send one out that will have more than one email address and the people do not know each other. You then put all other email addresses on the BCC line that way whoever receives the email only sees your email address on the TO line and no other email addresses.
It looks like this spammer is using this technique. At least they aren't beaming your email address out to tons of other people which could exacerbate the spam problem.
You've marked it as spam right? Some email programs and webmails can be set up to only allow (whitelist) email addresses you have approved. Popowich is going to set one up for me to test. I HATE spam and have a big problem with it too. I will let you know how it goes.