I used to work for an ad retargeting company. Our advertisers gave us a <i>ton</i> of data that we didn&#x27;t necessarily want along with pixel data that we did, including email addresses. So if you&#x27;re logged in to some retailers website and they were retargeting with us, they might either accidentally or deliberately passing us your email address, which would allow us (if we wanted to) to map your email address to your cookie. We see your cookie look at galleries, bam.<p>Or, more legally, the advertisers could be part of a specific email retargeting campaign where they give us your email addresses, and then we can establish the mapping in a more direct way.<p>Obviously there must have been more shading goings on in this case, but the principle is the same.