Why do old emails keep showing up as new in Mail?

I know Apple created this option where old emails could come back as reminder emails in Mail. I turned that off, but old emails for no particular reason keep showing up as new emails. Not just annoying but for many reasons dangerous in daily work. In litigation or negotiations it can be very important the date of an email. If Apple just hauls off and changes the date by creating it as a new email with a current date they are messing with things that should definitely not be messed with. Now, I can't even find where that old option of having old emails show up again was/is.

Apple needs to focus on fixing new and ancient problems, like names turning to all caps, instead of new features.

[Edited by Moderator]