Retention Policies when item gets deleted?

[Marcel Baschenegger]

Hello guys, 
I'm right now spinning my head around the following question, may you can assist.

Lets assume I have a retention policy (MRM) assigned to some mailbox which contains a tag 

- Tagtype: Default

- Retention period: 3 Years

- Action: Move to Archive

and no other policy except Deleted Items and Junkemail which are delete after 30 days.

Is it possible for an user to completely delete an email within the 3 years timeperiod from the inbox?

I know Email with assigned tags dont get deleted, BUT I'm not sure if ExO Folder assistant is assigning the Tag after the 3 years expired to them item as soon as the item is ready to get moved to the archive or before the 3 years expire so from the time the email arrives on.

I would like to save myself some time and dont review it with MFCMAPI. Maybe you can assist?

In case they are able to delete those items how is possible to prevent deletion of any mails? kind of when Litigation hold is assigned to a mailbox?

I don't want to use M365 Retention policies.

Could  a default tag be a solution with retention period: Hold indefintely and action:move to archive?

Best Regards

[#2 · Accepted solution]

Yes, it's possible. Old-style Exchange retention policies DO NOT preserve data and are not suitable for scenarios where you want to (immutably) store it for XXX days. They only address the "get rid of this items after XXX days" scenario.
If you want to prevent deletion, you need to apply some type of hold. Good old litigation hold will do just fine, in case you don't want to switch to the "modern" retention policies.