Catch/close "redundant" incidents that solve themselves?

Summary

Any ideas to recognize Incidents after customer reports issue is resolved?

Content

Hi All - in ecommerce, a large source of customer incidents is "Where's my order?" questions.  Sometimes after a customer submits an incident to us, they then discover the package has arrived, and they either send us a reply to our auto-reply, or send a separate message "never mind, found it"  (or something along those lines). 

Similarly, after an incident resolves, customer will often send a "Thanks!" email, which now appears as a newly reopened incident in our queue.

This all obviously increases unnecessary volume to our queues, and we are trying to come up with a way to recognize when this has happened, and set up a rule to automatically close that incident (or any related ones).    Even just a rule that allows someone to manually scan all incidents like this for "potential" redundancy would help us a lot.