What will happen to previously tracked / set regarding emails post upgrade to D365 and an Org URL change

Scenario -

1. Migrate CRM Orgs to D365 v9.0 on-Prem

2. The D365 on-Prem will have new URLs for each Org

3. Users will be migrated to use App for Outlook instead of the add-in

Question

Does anyone know what will happen to all existing emails that is already tracked into CRM Org?

I don't expect the CRM Record (picked by set regarding) link gets updated from within Outlook client.

But what will happen say if an email was already tracked, post migration, will any new message under that email trail gets tracked as expected?

Any ideas?

Regards

Xun