Shared mailbox email can't deleted on online achieve folder

First determine whether the messages return to their original Online Archive folder or remain only under Recover deleted items, because visible restoration and retained deleted copies require different fixes.

In Outlook on the web

1. Open the shared mailbox itself, then expand its Online Archive.
2. Delete the unwanted messages from the archive folder.
3. Open Deleted Items under that Online Archive, not the Deleted Items folder of your own mailbox or the shared mailbox’s primary mailbox.
4. If available there, select Recover items deleted from this folder and check whether the messages remain in the recovery list.
5. Check Settings > Account > Storage, if this page is available for the opened mailbox, to identify which visible folders consume space.^1^

Warning: Permanent deletion might be irreversible. Confirm that the messages are no longer required, and do not purge records covered by retention, legal hold, eDiscovery, or organizational recordkeeping requirements.

If the correct archive recovery view is available and no retention obligation applies, permanently delete the eligible items. Normal deletion only moves messages into Deleted Items, which continues consuming storage.^1^ Storage reporting can take approximately 24–48 hours to update after cleanup.^2^^3^

If Outlook on the web does not expose the archive’s Deleted Items or recovery location, ask an Exchange administrator to investigate it. Purging the primary mailbox’s recovery view does not establish that the archive’s separate deleted-item storage was cleared.

Exchange administrator checks

An administrator should connect to Exchange Online PowerShell using an account with permission to read mailbox configuration and statistics, then replace the example address below:

Get-Mailbox [Email] |
  Format-List ArchiveStat*,RetentionPolicy,*HoldEnabled

Get-Mailbox [Email] |
  Format-List ProhibitSendReceiveQuota,RecoverableItemsQuota

Get-MailboxStatistics [Email] |
  Format-List StorageLimitStatus,TotalItemSize,TotalDeletedItemSize

Get-MailboxFolderStatistics [Email] -Archive `
  -IncludeOldestAndNewestItems |
  Export-Csv .\archive-folder-stats.csv -NoTypeInformation

The first three commands identify archive state, the assigned retention policy, initial hold indicators, primary-mailbox quota status, and visible versus recoverable storage. The archive folder report identifies large archive folders and their applied DeletePolicy, ArchivePolicy, CompliancePolicy, and RetentionFlags.^4^^5^

TotalItemSize and TotalDeletedItemSize in this check describe the primary mailbox. The administrator must separately inspect the archive folder statistics and archive-specific service data rather than assuming that primary-mailbox figures represent the archive.

Apply the matching resolution

• Messages exist only in Recoverable Items: They have not returned to the original folder. Deleted items can remain recoverable until the deleted-item retention period expires.^6^
• A hold or Purview retention policy applies: Permanently deleted content may still be preserved in Recoverable Items. Do not remove or weaken the hold merely to reclaim storage. The displayed *HoldEnabled properties are only an initial check; the compliance administrator should also review Purview retention policies, labels, eDiscovery cases, and other preservation settings.^6^
• Messages visibly return to their original archive folder: A hold alone does not explain that visible movement. Check the shared mailbox under Settings > Mail > Rules, and review server-side rules, retention tags, and processes used by other delegates or Outlook clients. Rules created elsewhere might not appear to the user and may require Exchange administrator review.^7^
• A retention policy was just corrected or assigned: Run the Managed Folder Assistant, wait at least one hour, and check again:

Start-ManagedFolderAssistant [Email]

Exchange Online processing can otherwise take up to seven days, and large mailboxes can process more slowly.^5^

• The archive is genuinely at its licensed limit: Verify the shared mailbox has an archive-capable license. An unlicensed shared mailbox is limited to 50 GB; use or expansion of its Online Archive requires the applicable Exchange Online Plan 2 or Exchange Online Plan 1 plus Exchange Online Archiving license. Assign the license through your organization’s Microsoft 365 licensing administration, then enable the supported archive capacity or auto-expanding archiving as appropriate.^8^

If the archive folder statistics, retention configuration, and rules do not explain the visible restoration, open a Microsoft 365 support request so Microsoft can inspect mailbox-side processing.

References

1. [Web](https://support.microsoft.com/outlook/mailbox-storage-limits-in-outlook#other-ways-to-reduce-your-storage)
2. Outlook Memory Full Issue – Unable to Send/Receive Emails - Microsoft Q&A
3. Mailbox size issue - Microsoft Q&A
4. "Mailbox is full" warning even if the mailbox hasn't reached the storage limit
5. Resolve email archive and deletion issues when using retention policies
6. Retention tags and retention policies in Exchange Online
7. someone has put a rule in a shared mailbox however we cannot see the rule in order to delete - Microsoft Q&A
8. Exchange Online limits