- Outlook’s new auto-archive kicks in when your mailbox reaches 90% capacity
- Existing data retention and archiving policies are not affected
- Auto-expanding files are also on the horizon
Microsoft will soon begin rolling out a new threshold-based automatic archiving for Exchange Online in a bid to prevent “mailbox full” errors.
The feature will work by automatically archiving older items when storage capacity reaches 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 approached 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 companies’ existing archiving policies; Instead, it acts as a safety mechanism when space is limited. The “Never move to archive” label will also be honored, keeping those emails in the main inbox.
Automatic archiving also won’t interfere with data retention and deletion policies, because emails will still be stored in the archive.
However, users will not be able to turn off automatic archiving. “It is a fail-safe mechanism to avoid interruptions in the flow of mail and is only activated when mailbox utilization exceeds the (critical) threshold of 90%,” the company explained.
A separate Microsoft roadmap entry, tracked as 395793, details efforts to support files that automatically expand beyond the normal 100GB quota limit. The launch is imminent, according to the note.
An October 8 update to the blog post notes that a revised release plan for automatic archiving will be communicated “in the near future” as a result of customer feedback. As of this writing, the October 7 blog post has not been updated.
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