Years ago I did some research with email and found that you could set the preview time to never update so that in a sense you could read the email in the preview tab without triggering the read/unread update.
Also, I am pretty sure that if you read an email and then change back to unread there is a date change or update flag. We were using Outlook Spy and I think it was fairly convincing evidence.
For read requests there are settings to never respond which I routinely set.
I would set up a test environment and run through the possibilities.
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