Microsoft enables Exchange Online auto-archiving by default

Microsoft is rolling out threshold-based auto-archiving for Exchange Online that automatically moves the oldest items to users' archive mailboxes when primary mailbox utilization nears 90% to prevent mail flow disruption; the feature will be enabled by default after rollout (public clouds this month, government clouds in November), honors a 'Never Move to Archive' flag, and the announcement also notes related Defender for Office 365 updates to detect email-bombing attacks. The content is an operational/product update rather than a report of an active security incident.