Treat your personel email address that you have from ISP as Gold dust, dont dish it out filling any sort of forms, only for personal communication, you can open an account with lots of browser based emails ie; Yahoo, Hotmail, Gmail etc etc and use them for all other stuff you want to do.
The spammers use Web Crawler Programs to fish for emails addresses from the WWW, if you dont have decent Firewall, they will also know what are your interest are through the various cookies embeded and unknowingly downloaded while browsing and then you will be bombarded with spam emails for those interests of yours..
As mentioned here earlier, if you right click the email, and see the properties, that should give you a path or source of the email sent to you.
you can than find the domain, google domain to ip address resolution and you will be able to find ISP, from here on you can inform the domain about the spammer at abuse@.... but its not going to make much diffrence.