If you really want to use email for this, there are three possible solutions (which can also be combined):
Create a new email address and make sure the sender uses a script that hides the email address from everything else. I have done this for web forms, and I have never received any extra emails.
Have your send append something like "[OK]" to the subject, and then use Outlook's filters to delete all other emails.
Use encryption (you will need to give a public key to your sender) and discard all the other emails (again using Outlook's filters).
All of these ideas require you to "educate" your preferred sender in some way. If this is not possible, I'm afraid you will have to resort to using something other than Outlook (some sort of peer to peer technology, for example).
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