How Exchange Online Uses Archives to Offload Recoverable Items Storage

Odd Title for Notification, but Real Value in Update

What does “Exchange online auto-expanding archive–Automatic archive of mailbox items in Purges, Versions and Discovery Holds folders” mean? That’s exactly what I thought when I read message center notification MC288630 (1 October). It’s a classic example of how poor editing can mask the value in a message. Here’s what’s happening.

The Recoverable Items structure is composed of several sub-folders, each with a distinct task. A set of sub-folders within Recoverable Items are used for retention processing:

  • Purges: Stores items removed from the Deletions folder.
  • Versions: Stores the original versions of edited items.
  • DiscoveryHolds: Contains hard-deleted items.
  • SubstrateHolds: Contains the original versions of items managed by the Microsoft 365 substrate (for example, compliance items for Teams messages).

If a mailbox doesn’t come within the scope of a litigation or in-place (retention) hold, you won’t see items in these folders. You will see items in the Deletions folder because this is where items removed from the Deleted Items folder go until Exchange Online removes them permanently. Items stay in Deletions for the deleted items retention period defined for a mailbox (usually 14 days but can be changed to a maximum of 30 days). During this period, users can recover items from Deletions using Outlook’s Recover Deleted Items option. For more information on how these folders are used, see this Microsoft article.

Cluttering Up Recoverable Items

The point of retention policies is to keep information for as long as it is needed. Although Microsoft allocates a 100 GB storage quota to store data in Recoverable Items when a mailbox is subject to retention, it’s not uncommon to find that some mailboxes accumulate information quickly and occupy the quota. The change described in MC288630 and being rolled out in mid-October aims to take advantage of archive mailboxes by moving information from the Purges, Versions, and DiscoveryHolds sub-folders to the archive mailbox one day after their generation.

In effect, this is the same processing as would occur if you were able to assign a 1-day move to archive Exchange retention tag to these folders. The Managed Folder Assistant looks at the contents of the folders when it processes a mailbox and, if the mailbox has an archive, applies the one-day move to archive rule. The same processing occurs for both normal and auto-expanding archives.

The net effect is that the space occupied by the items in these folders in primary mailboxes is reduced dramatically and administrators won’t have to step in as often as happens now to remove data from Recoverable Items. The items moved into the archive remain indexed and discoverable and have the same value for retention processing.

Ignoring Existing Policies

MC288630 says that “existing archiving policies created by customers for these folders will be ignored” once the change is effective. In other words, if you have an Exchange retention policy with a folder tag for the Recoverable Items folder which takes another action (for instance, for move to the archive after 90 days), the Managed Folder Assistant will now ignore the folder tag when it processes the Purges, Versions, and Discovery Holds sub-folders. However, the folder tag (or a default move to archive tag) will apply to items in the Deletions sub-folder.

Users will remain blissfully unaware of the change. They can’t access the three sub-folders in either primary or archive mailboxes. This is simply a matter of moving data around to a new location to make the overall functioning of the Recoverable Items structure in primary mailboxes more effective. It’s a good change.


So much change, all the time. It’s a challenge to stay abreast of all the updates Microsoft makes across Office 365. Subscribe to the Office 365 for IT Pros eBook to receive monthly insights into what’s happening.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.