A change rolling out in mid-October will remove storage pressure on the Recoverable Items structure in Exchange Online mailboxes by offloading some data to archive mailboxes. The idea is a good one because it means that the storage allocated to Recoverable Items won’t fill up and require intervention so often. Users won’t know anything about what’s happening under the covers as it’s all hidden from view.
https://office365itpros.com/2021/10/05/how-exchange-online-uses-archive-mailboxes-clean-up-recoverab...
