My company is instituting an email retention policy and it was done without input from anyone technical. Here is what they want to do, they want to put a folder in every user's mailbox called Archive (but this is not an Exchange Archive folder).  Then they want email that the user places in that folder to never be purged.  They want all other email (any other folders besides "Archive" in the mail box) to be deleted after 24 months.  

I have been searching for a week to find a way to do this, but haven't come up with anything.

Ask them how much money they've got.

This is what you have.

https://technet.microsoft.com/en-us/library/dd335093(v=exchg.150).aspx

You should understand this thoroughly so that you're in a position to tell your management exactly what they can and can't have without spending millions of dollars writing custom code.