Whether they're tracking for cookies or not, it's best to use Gmail to stop any tracking eBay has with their emails. Just use Gmail and don't worry about it.
I'm an email marketer as well; I send thousands of emails to customers a week. I enable tracking for my emails, which is a 1 pixel image within an email. It lets me know if someone opens an email, and if they clicked on a link, which helps me for marketing. What eBay does with their tracking no one knows for sure. Again, be safe and use Gmail which blocks all images by default and thus protecting you.
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