Hey @Brenden Keane,
I have had my share of headaches rolling this out for a client, and trying to get it to work in the timeframe you wanted.
MRM policies are tied directly to the Managed Folder Assistant (MFA) in exchange online
As my friend @Vasil Michev pointed out, the MFA only runs ones roughly every 7 days (although its not like its sitting there and at 1am on a Monday always runs.) So if you go through an apply a policy to a users mailbox on say a Monday. That Thursday maybe the policy runs. The following Friday your users goes through and tags stuff with the new policy. Well it could be later in the following week before you see any changes to the stuff they taged.
In our experience it was just really really hard to know exactly when/if it was working.
You can however essentially ask that your mailbox be put in the queue to run the MFA on the EXO servers:
Start-ManagedFolderAssistant -Identity "Mailbox"
This works great for initial testing, but not long term. So why you are trying to confirm your MRM policy is working/for this user. Go in and run the above command once you know the policy has been applied, and a short time later (Probably 30 min to a few hours depending on the Microsoft Queue,) you should see the application to that mailbox.
Note this command is really meant to just do something like mention above, testing. If you do it repeatedly, (like write a script to try to do this once a day) you will get throttled.
So for your testing, once the policy is on, run that command and see if you have success.
Goodluck!
Adam
