In addition to what was already suggested, I also look at trends for people who have clicked every link in our emails -- especially if those users have something in common.
While you should always be looking at results with the lens of what's typical for your audience and not necessarily someone else's, for us, I would say it's very rare that someone would click every link, including header/footer/social links. So, if I see something like that come in, I'll also look to see if, say, those users are all from the same company. If that's the case, you might consider that activity coming from these users is a result of a spam checker or something of that sort.
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