First of all, I have to say that this announcement has a trick, is it possible to do it, but not by the UI, you need to open a Microsoft ticket support in order to do it (I supose that in a near future will be avalaible trought the UI admin).
To open the support ticket, would be necessary to have the following data:
- The default domain name of your Office 365 organization.
- The tenant name and tenant ID of your Office 365 organization.
- And of course a title or description of the purpose of the support request: for example “Enable Application Content Search for On-premises Users”. This will help route the request to the Office 365 eDiscovery engineering team who will implement the request.
Also take into account that Teams channel conversations are always into Group mailboxes which are always in the cloud, so probably would be not possible to extract this information from the chat for those users who are in a hybrid environment and their Exchange data resised OnPrem.
Then after the ticket has benn submmited, I hope that Support will send us an email, and they will process the request internally.
For more info about this: https://support.office.com/en-us/article/searching-cloud-based-mailboxes-for-on-premises-users-in-office-365-3f7dde1a-a8ea-4366-86da-8ee6777f357c?ui=en-US&rs=en-US&ad=US