How to Enable Exchange Online Mailbox Archives Based on Mailbox Size

This article explains how to use PowerShell to enable Exchange Online archive mailboxes after primary mailboxes reach a certain size. Some simple PowerShell code checks the mailbox size and if it's too large, enables the archive and assigns a mailbox retention policy containing a default move to archive tag to move items from the primary to the archive mailbox. Some Azure Automation would make sure that the script runs periodically to keep mailboxes in good health.