Thank you for your answers.
I get it a little, and specifically that we can't go back to our old way of working.
We've had some frustrating trouble with Outlook over the years, starting with overflowing data and crashing mailboxes because of that.
The solution for that was storing our email per year in different pst files, one for every year since 1998.
By opening all these files simultanuously in Outlook, we were able to view and search through all our mails since then.
Which comes in handy for a small company as ours : a well organised database.
Backups we make weekly on different systems like for example USB sticks which are stored in different places.
I've tried to start a ticket in the admin center, but if I look for example on "backup" or "export email" I don't get the right hits.
I don't see it.
Is it possible to export our Outlook-online-emails to a pst file ?