I came across this question in which a moderator noted that a user had a "same IP diff email". I was under the impression that our e-mail was only visible to us or used for the purposes explained in the input field help tip:
If this is the case, I think users should know this and moderators have different tools to determine duplicate user accounts.
Edit: it was mentioned in this answer and in this answer that mod's have visibility, but it doesn't seem like it's very publicized. I'm finding this out after using the site after 3 years (perhaps I was a bit naive).