Content reviewed: 29 October 2026
Outlook reports a full mailbox even though ordinary mail occupies only 18 GB of a 100 GB quota. The user empties Deleted Items, but the problem continues. The administrator then finds more than 100 GB in Recoverable Items. These are not two views of the same capacity: Exchange Online uses separate quotas for ordinary content and recoverable items.
When Recoverable Items is full, establish the actual quota, why the data is being retained and whether its transfer to the archive works. Adding a licence, emptying Deleted Items or having a large online archive does not prove the problem is resolved. This guide takes you from measurement to outcome checks, including the differences between 100, 105 and 110 GB limits and the new capacity of up to 3 TB for certain archives.
Three storage areas to distinguish
Visible Outlook content, hidden Recoverable Items and the online archive have different purposes. An Archive folder inside the ordinary mailbox is also different from a separate Online Archive. During an incident, identify where the items are actually stored.
| Area | Typical content | What its size does not prove |
|---|---|---|
| Ordinary primary mailbox content | Inbox, Sent Items, Calendar and Deleted Items | Free space here does not exclude full Recoverable Items |
| Primary mailbox Recoverable Items | Recoverable deleted items, preserved copies and other internal content | This is not spare capacity freely available for ordinary mail |
| Online archive, including its Recoverable Items | Moved items and associated retained content | Free archive space does not guarantee items are moving from the primary mailbox |
Microsoft's Recoverable Items documentation explains the separate quota and the Deletions, Purges, Versions and DiscoveryHolds subfolders. Their names help identify the growth mechanism. Finding the largest folder, however, does not establish that its contents should be deleted.
Why deletion may not release space
Deleting a message can simply change where it is retained. Where retention or a hold applies, a preserved copy remains available for that purpose. Even a mailbox that an application regularly empties can develop this problem: little visible mail does not mean little retained data.
Distinguish two uses of the word retention. Exchange MRM can move older items into an archive. Purview retention and eDiscovery holds preserve content. Configuring an archive move does not itself remove the requirement to keep the data. Microsoft's current guidance for mailboxes on hold describes moving Recoverable Items from the primary mailbox to the corresponding archive area, rather than removing evidence.
Turning off a hold or setting deleted-item retention to zero should therefore not be the default fix. First identify the policy owner and retention purpose. Any change to that requirement is a separate substantive decision, rather than a routine way to free storage.
What 30, 100, 105 and 110 GB mean
The baseline limits appear in Exchange Online service limits. Archiving extensions must be read alongside the configuration of the particular mailbox. The following values are not four capacities that administrators can choose freely.
| Primary Recoverable Items configuration | Documented value | Diagnostic use |
|---|---|---|
| Standard mailbox without a hold | 30 GB | Separate baseline quota; do not infer it from Inbox size |
| Applicable hold or retention policy | 100 GB | Identify the retention mechanism actually applied |
| Archive enabled for a mailbox on hold or assigned a retention policy | 105 GB | Additional archiving headroom, not a multiplied primary mailbox size |
| Individual auto-expanding archive enablement for an applicable mailbox | 110 GB | Conditional operating headroom; differs from organisation-wide enablement |
The difference between individual and organisation-wide enablement is easily missed. The auto-expanding archive setup guide states that organisation-wide enablement does not itself add the same 10 GB as the individual operation for a mailbox on hold. The user's AutoExpandingArchiveEnabled property may also remain False after organisation-wide enablement. Reading one property in isolation is insufficient.
During an incident, use the actual RecoverableItemsQuota and RecoverableItemsWarningQuota values, archive status and organisation configuration. The table explains the mechanism; it does not replace measurements from the tenant.
A 3 TB archive is not a 3 TB primary mailbox
In October 2026, Microsoft announced an increase in the maximum auto-expanding archive from 1.5 TB to 3 TB for specified eligible licences. The current archive capacity overview says rollout began in mid-October, with completion planned for late October. As of this review date, that does not confirm completion in every tenant.
Eligible offers include Microsoft 365 E5, Office 365 E5 and Microsoft 365 Purview Suite. For E5, the documentation requires the relevant Records Management service plan to remain enabled. Other licences do not automatically qualify for 3 TB. Nor is 3 TB assigned as free space upfront: the archive expands incrementally.
The diagnostic implication is different: a higher archive maximum does not enlarge primary Recoverable Items to terabytes. A fix must address the transfer path, available archive capacity and processing time. If hidden primary storage is full today, a future archive expansion will not restore service by itself.
Read-only diagnostics
Start with read-only queries using Exchange Online PowerShell and appropriate mailbox administration permissions. Replace user@example.com with the mailbox being investigated. The following queries inventory the configuration; they do not change it.
- Inspect mailbox type, quotas, archive and hold settings with
Get-Mailbox -Identity user@example.com, then review the relevant properties. LitigationHoldEnabled=False alone is not a complete inventory of retention policies. - Check primary size with
Get-EXOMailboxStatistics -Identity user@example.com. Use the supported-Archiveswitch for the archive. - Inspect Recoverable Items with
Get-EXOMailboxFolderStatistics -Identity user@example.com -FolderScope RecoverableItems. Add-Archivefor the corresponding archive scope. - Record the query date and compare FolderSize, FolderAndSubfolderSize and item counts. Repeat measurements at a defined interval to distinguish sustained growth from a one-off change.
The parameters are documented separately in Get-EXOMailboxStatistics and Get-EXOMailboxFolderStatistics. We checked these commands against the documentation for this article; we did not execute them against customer data.
Do not add a parent FolderAndSubfolderSize aggregate to its child aggregates: the same items would be counted repeatedly. Check the internal search-processing subfolders under DiscoveryHolds separately. Microsoft notes that certain such folders do not contain recoverable mailbox content and do not count towards the quota. Large values in individual rows cannot simply be added into one storage total.
Turn measurements into a decision
The following working model is an editorial illustration, not a customer measurement. All sizes use the same GB unit for simplicity.
| Indicator | Illustrative value | Implication |
|---|---|---|
| Visible primary mail | 18 of 100 GB | A larger primary mailbox does not explain the incident |
| Recoverable Items | 101 of the actually configured 105 GB | 4 GB of operating headroom remains |
| Net Recoverable Items growth | 0.4 GB per day | About 10 days remain if the trend is unchanged |
| Archive | 70 of its initial 100 GB | Space exists, but transfers and expansion conditions need checking |
The calculation free capacity / net daily growth is a planning aid rather than a precise forecast. Changes in activity, attachments or retention may alter the trend. It nevertheless gives the accountable team a more useful deadline than waiting to see whether the archive starts working.
If ten remaining days are insufficient for a verified fix and potential support case, escalate immediately. Provisioning extra auto-expanding archive capacity can take up to 30 days. Enablement is also irreversible and affects later handling of an inactive mailbox. It should not be a thoughtless bulk response to every mailbox-full alert.
Verify the transfer, not just command completion
The newer threshold-based auto-archiving differs from automatic archive expansion. Documentation describes transfers above a 96% threshold, an existing archive with free space and independent checks of primary and Recoverable Items quotas. It also lists exceptions, including overly recent items and Never Move to Archive tags. The page still references preview, so verify availability in your environment.
Several signals should agree after remediation: the correct quota decreases, the corresponding archive area grows, processing succeeds and the affected user workflow works again. Test receiving mail, calendar activity and deletion using a nonproduction test item. Starting Managed Folder Assistant does not prove the transfer has completed.
If sizes do not change, prepare a time series, current quotas, archive status, relevant policies and exact symptoms for support. Refer retention decisions to the policy owner. Related licensing is covered in Shared mailbox: licences and archive; the distinction between preservation and recovery is explained in Retention, archive and backup.
Frequently asked questions
Why does emptying Deleted Items help only briefly or not at all?
Items may move into Recoverable Items and remain preserved under applicable retention. Identify which quota is full first. Deleting visible mail does not mean its preserved copies disappear.
Does E5 enlarge Recoverable Items to 3 TB?
No. The new maximum applies to an eligible auto-expanding archive, including its retained content. Primary Recoverable Items has a separate quota. Check rollout and enabled licence components too.
Are auto-archiving and auto-expanding archiving the same?
No. The former moves eligible items based on utilisation; the latter adds archive capacity incrementally. Establish which mechanism you need and whether its prerequisites are met.
Does a False value mean the archive is disabled?
The AutoExpandingArchiveEnabled property alone is insufficient. Organisation-wide enablement may not change the user property to True. Distinguish archive existence, user-level enablement and organisation settings.
Should we remove a hold to restore service?
Not as an automatic first step. It may preserve content for a specific case or retention requirement. Map policies, archiving and quotas first. Removing preservation needs a separate approved decision and an appropriate process.
