Exchange Online will start archiving your oldest emails before your inbox bursts

Microsoft promises fewer 'mailbox full' errors in face of message deluge

Microsoft's latest attempt to make the dreaded "mailbox full" response a thing of the past is rolling out in October and November. Threshold-based auto-archiving is coming to Exchange Online.

The plan, which Microsoft refers to as "reimagining archiving," involves automatically moving the oldest items from a user's primary mailbox to an archive location when the mailbox approaches 90 percent of its quota.

Time-based archive policies – such as "move to archive after two years" – are useful for some, but can't keep up with increasing volumes of incoming emails, large attachments, and the relentless tsunami of AI-generated content (Microsoft cites Copilot as an example, which will generate emails containing meeting notes, automated reports, notifications, and so on).

"As a result, mailboxes can reach full capacity before time-based archiving kicks in, leading to functional loss such as inability to send or receive emails directly impacting business continuity and operational efficiency," Microsoft wrote in a blog post.

Microsoft's solution is threshold-based archiving, which will shunt the oldest items to the archive, except for those marked with the "Never Move to Archive" tag set. An archive mailbox still needs to be provisioned and have sufficient space – there is no auto-expanding here, and the process is intended only as a failsafe.

Administrators will be interested to learn that the function will also temporarily override the current archiving policy and cannot be turned off if archiving is already enabled. This is something to keep in mind when the support calls come rolling in from users with bulging mailboxes wondering where messages have gone.

Folder structure is preserved, and messages remain searchable and accessible. It will have simply been moved to the provisioned archive mailbox.

The update is due to become generally available in the public cloud on October 15 and will roll out to government clouds in November. ®