How Can a Site's Cookies Find out My Email Address?

Hi, I have been researching a new market, and found an informative post on a forum for sellers in this market. I visited the forum ONCE, two days ago. And I only looked at one thread, about pricing and ROI. I did not register at all. I was just browsing.

Today I got an email from a spammer (not picked up by Gmail's spam filter) trying to sell a product that is totally unrelated to the forum. But the thing that concerns me is; the email it is from, is in the following format:

(exact forum domain)@----.com

So it looks like my personal details were collected when I visited the site.

Is this possible?

I knew about regular cookies, but not happy about my personal email being collected. What the hell else are they collecting?!

I don't know if I am being paranoid or naive!

And how can I avoid this happening in the future? (without anonymous browsing? - I looked into that once and it seemed a lot of trouble to go to).

Or does it mean I have a virus or malware?

Thanks a lot