I think you’re greatly mistaken in your assumptions. Harvard would suffer much greater damage to their reputation if they honored a fake acceptance email. To my knowledge, no university has ever honored a fake (physical) acceptance letter either, and those have existed (as pranks or otherwise) for a while.

It’s highly unlikely that such a case would even get to trial without being dismissed. For example, see this Quora thread [1] about the case of the university itself sending out the actual acceptance letter. Columbia University also had an incident where a system error accidentally sent out acceptance emails, which they quickly retracted, and no lawsuit or settlement came out of that.

I think it would be incredibly difficult to prove damages in such a case, especially since a fake acceptance letter doesn’t prevent you from going to another college. Your example of the student withdrawing their other applications is also unlikely to be blamed on Harvard, particularly before the student has officially accepted (at which point Harvard would notice they didn’t accept the student).

[1] https://www.quora.com/Can-a-university-be-sued-if-it-first-s...