- Outlook’s new automatic archiving kicks in when your mailbox reaches 90% capacity
- Existing archiving and data retention policies are not affected
- Auto-expanding archives are also on the horizon
Microsoft will soon begin rolling out new threshold-based automatic archiving for Exchange Online in an effort to prevent “mailbox full” errors.
The feature will work by automatically archiving older items when storage capacity reaches maximum capacity, marking a shift from time-based archiving (such as “move after two years”) as email volume and attachment sizes continue to grow.
Public cloud customers will see the change in October 2025, and government clouds will receive the update in November.
Outlook will automatically start archiving old emails
The Exchange team explained in a blog post that older emails would be automatically archived once the mailbox quota approaches 90%. This comes from feedback that users wanted “proactive and automated space management” solutions.
Microsoft emphasized that automatic archiving does not replace or interfere with existing company archiving policies; rather, it acts as a safety feature when space becomes tight. The “Never move to archive” tag will also be honored, keeping these emails in the primary inbox.
Auto-archiving will also not interfere with data deletion and retention policies, as emails will still be stored in the archive.
However, users will not be able to turn off auto-archiving. “This is a security mechanism to prevent any interruption in mail flow and is only triggered when mailbox usage exceeds the (critical) threshold of 90%,” the company explained.
A separate Microsoft roadmap entry, numbered 395793, details efforts to support auto-expanding archives beyond the normal 100 GB quota limit. Rollout is imminent, according to the memo.
An October 8 blog update states that a revised release plan for auto-archiving will be communicated “in the near future” following customer feedback. At the time of writing, the October 7 blog post has not been updated.
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