What kind of sorcery is this? [View all]

I am aware that sometimes if you search for things on the internet you will start getting ads of the items you were searching for....

But yesterday I was on 2 web sites looking at sneakers. One was Saucony and the other was Allbirds. 2 legit sites. I looked around for a few minutes. Today I had an e-mail from each of these sites. How did they get my e-mail address?

I marked them as spam and didn't open them.

I'm baffled as to how they got my email.