Overview:
In Microsoft 365 Business Premium (Exchange Online), data protection features are in place to help recover emails or other mailbox items that have been accidentally deleted or gone missing. When an item is deleted, it passes through stages before being permanently removed. By default, deleted items are retained for 14 days (configurable up to 30 days by an administrator). During this period, both end users and administrators have multiple methods to restore deleted emails, contacts, calendar events, and tasks. This guide outlines all recovery methods for both users and admins, assuming the necessary data protection settings (like retention policies or single item recovery) are already enabled.

Deletion Stages in Exchange Online

Understanding how Exchange Online handles deletions will inform the recovery process:

• Deleted Items Folder (Soft Delete): When a user deletes an email or other item (without using Shift+Delete), it moves to the Deleted Items folder[1]. The item stays here until the user manually deletes it from this folder or an automatic policy empties the folder (often after 30 days)[2].

• Recoverable Items (Soft Delete Stage 2): If an item is removed from Deleted Items (either by manual deletion or “Empty Deleted Items” cleanup) or if the user hard-deletes it (Shift+Delete), the item is moved to the Recoverable Items store (a hidden folder)[1]. Users cannot see this folder directly in their folder list, but they can access its contents via the “Recover Deleted Items” feature in Outlook or Outlook Web App.

• Retention Period: Items remain in the Recoverable Items folder for a default of 14 days, but administrators can extend this to a maximum of 30 days for each mailbox. This is often referred to as the deleted item retention period. Exchange Online’s single item recovery feature is enabled by default, ensuring that even “permanently” deleted items are kept for this duration[1].

• Purge (Hard Delete): Once the retention period expires (e.g., after 14 or 30 days), the items are moved to the Purges subfolder of Recoverable Items and become inaccessible to the user[1]. At this stage, the content is typically recoverable only by an administrator (and only if it’s still within any hold/retention policy). After this, the data is permanently deleted from Exchange Online (unless a longer-term hold or backup exists).

With this in mind, we’ll explore recovery options available to end users and administrators.

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Recovery by End Users (Self-Service Recovery)

End users can often recover deleted mailbox items on their own, using Outlook (desktop or web). This includes recovering deleted emails, calendar appointments, contacts, and tasks, provided the recovery is attempted within the retention window and the item hasn’t been permanently purged. Below are the methods:

1. Restore from the Deleted Items Folder (User)

When you first delete an item, it moves to your Deleted Items folder:

1. Check the Deleted Items folder: Open your mailbox in Outlook or Outlook on the Web (OWA) and navigate to the Deleted Items folder[2]. This is the first place to look for accidentally deleted emails, contacts, calendar events, or tasks.

   • Items in Deleted Items can simply be dragged back to another folder (e.g., Inbox) or restored via right-click > Move > select folder[2]. For example, if you see the email you need, you can move it back to the Inbox. If a deleted contact or calendar event is present, you can drag it back to the Contacts or Calendar folder respectively.
     

   • Tip: The Deleted Items folder retains content until it’s manually cleared or automatically emptied by policy. In many Office 365 setups, items may remain here for 30 days before being auto-removed[2]. So, if your item was deleted recently, it should be here.

2. Recover the item from Deleted Items: Select the item(s) you want to recover, then either:

   • Right-click and choose Move > Other Folder to move it back to your desired location (such as Inbox or original folder)[2].
     

   • Or, in Outlook desktop, you can also use the Move or Restore button on the ribbon to put the item back.
     

   • The item will reappear in the folder you choose, effectively “undeleting” it.

3. Verify restoration: Go to the target folder (Inbox, Contacts, Calendar, etc.) and ensure the item is present. It should now be accessible as it was before deletion.

If the item is found and restored at this stage, you’re done. If you emptied your Deleted Items folder or cannot find the item there, proceed to the next method.

2. Recover from the Recoverable Items (Hidden) Folder (User)

If an item was hard-deleted or removed from Deleted Items, end users can attempt recovery from the Recoverable Items folder using the Recover Deleted Items feature:

1. Access the “Recover Deleted Items” tool:

   • In Outlook on the Web (browser): Go to the Deleted Items folder. At the top (above the message list), you should see a link or option that says “Recover items deleted from this folder”[2]. Click this link.
     

   • In Outlook Desktop (classic): Select your Deleted Items folder. On the ribbon, under the Folder tab, click Recover Deleted Items from Server[2]. (In newer Outlook versions, you might find a Recover Deleted Items button directly on the toolbar when Deleted Items is selected.)

2. View recoverable items: A window will open listing items that are in the Recoverable Items folder and still within the retention period. This can include emails, calendar events, contacts, and tasks that were permanently deleted[2]. All items are shown with a generic icon (usually an envelope icon, even for contacts or calendar entries)[2].

   • Tip: Because all item types look similar here, you may need to identify items by their subject or other columns. For instance, contacts will display the contact’s name in the “Subject” field and have an empty “From” field (since contacts aren’t sent by someone)[2]. Calendar items or tasks might show your name in the “From” column (because you’re the owner/creator)[2]. You can click on column headers to sort or search within this list to find what you need.

3. Select items to recover: Click to highlight the email or other item you want to restore. You can select multiple items by holding Ctrl (for individual picks) or Shift (for a range). In OWA, there may be checkboxes next to each item for selection[2].

4. Recover the selected items: In the recovery window, click the Recover (or Restore)** button (sometimes represented by an icon of an email with an arrow). In Outlook desktop, this might be a button labeled “Restore Selected Items”[2]; in OWA, clicking Restore will do the same.

   • What happens next: The recovered item(s) will be moved back into your mailbox. Recovered emails and other items from this interface are typically restored to your Deleted Items folder by default[2]. This is by design: you can then go into Deleted Items and move them to any folder you like. (It prevents confusion of plopping items directly back into original folders, especially if those folders didn’t exist anymore.)

5. Confirm and move items: Navigate again to your Deleted Items folder in Outlook. You should see the items you just recovered now listed there (they usually appear as unread). From here, move the items to their proper location:

   • For an email, move it to Inbox or any mail folder.
     

   • For a contact, you can drag it into your Contacts folder.
     

   • For a calendar appointment, drag it to the Calendar or right-click > Move to Calendar.
     

   • For a task, move it into your Tasks folder.
     The item will then be fully restored to its original type-specific location.

6. Troubleshooting: If you do not see the item you need in the Recover Deleted Items window, it might mean the retention period has passed or the item is truly gone. By default, items are only available here for 14 days unless your admin extended it[1]. In some setups it could be up to 30 days. If the item is older than that, end users cannot recover it themselves[1]. In such cases, you should contact your administrator for further help – administrators may still retrieve the item if it was preserved by other means (see Admin Recovery below).

Summary of User Recovery: A user should always first check Deleted Items, then use Recover Deleted Items in Outlook/OWA. These two steps cover the majority of accidental deletions. The user interface handles all common item types (mail, calendar, contacts, tasks) in a similar way. Remember that anything beyond the retention window (e.g., >30 days) or content that was never saved (e.g., unsaved drafts) cannot be recovered by the user and would require admin assistance or may be unrecoverable.

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Recovery by Administrators (Advanced Recovery)

Administrators have more powerful tools at their disposal to help recover missing or deleted information from user mailboxes. Admins can recover items that users can’t (such as items beyond the user’s 14/30-day window or items from mailboxes that are no longer active). Below are the methods for administrators:

1. Recover Deleted Items via Exchange Admin Center (EAC)

Microsoft 365 administrators can use the Exchange Admin Center to retrieve deleted items from a user’s mailbox without needing to access the user’s Outlook. This is useful if the user is unable to recover the item or if the admin needs to recover data from many mailboxes.

Steps (EAC Admin Recovery):

1. Open the Exchange Admin Center: Log in to the Microsoft 365 Admin Center with an admin account. Navigate to the Exchange Admin Center (EAC). In the new Microsoft 365 Admin portal, you can find this under Admin centers > Exchange.

2. Locate the user’s mailbox: In EAC, go to Recipients > Mailboxes. You will see a list of all mailboxes. Click on the mailbox of the user who lost the data. This opens the properties or a details pane for that mailbox.

3. Select “Recover deleted items”: In the mailbox properties, find the option for recovery. In the new EAC, there is often an “Others” section or a context menu (•••). Click that and then click “Recover deleted items”[1]. (In older versions of EAC, this might appear as a link or button directly labeled “Recover deleted items.”)

   • The EAC will load a tool that is very similar to what the user sees in Outlook’s recover interface. It may show the most recent 50 recoverable items by default[1], along with search or filter options.

4. Find the items to recover: Use the interface to locate the missing item(s). You can filter by date range, item type (mail, calendar, etc.), or search by keywords (subject, sender) to narrow down the list[1]. This helps when there are many deleted items. All items that are still within the retention period (and thus in the user’s Recoverable Items folder) should be visible here.

5. Recover the item(s): Select the desired item(s) from the list, then click the Recover button (sometimes shown as a refresh or arrow icon). Confirm the recovery if prompted. The Exchange Admin Center will restore those items back to the user’s mailbox.

   • Where do they go? Just like when a user does it, the recovered items through EAC will be returned to the user’s Deleted Items folder (this is the default behavior)[2]. The user (or admin) can then move them to the appropriate folder afterward.

6. Notify the user: It’s good practice to inform the user that the items have been recovered. The user should check their Deleted Items folder for the restored data[2] and move it back to the desired location.

Note: To use the EAC recovery feature, the admin account needs the proper permissions. By default, global admins have this. If an admin cannot see the “Recover deleted items” option, they may need the Mailbox Import-Export role added to their account’s role group[1] (this role is required for mailbox recoverable item searches).

2. Recover via PowerShell (for Admins)

For more advanced scenarios or bulk recoveries, admins can use Exchange Online PowerShell. Microsoft provides two key cmdlets for deleted item recovery: Get-RecoverableItems (to search for recoverable deleted items) and Restore-RecoverableItems (to restore them)[3][3]. This method is useful if you want to script the recovery, search with complex criteria, or recover items from multiple mailboxes at once.

Steps (PowerShell Admin Recovery):

1. Connect to Exchange Online via PowerShell: Launch a PowerShell session and connect to Exchange Online. Use the following steps (requires the Exchange Online PowerShell module or Azure Cloud Shell):

   Connect-ExchangeOnline -UserPrincipalName admin@yourtenant.com

Log in with your admin credentials. Once connected, you can run Exchange Online cmdlets.

2. Search for recoverable items: Use Get-RecoverableItems to identify the items you want to restore. At minimum, you provide the identity of the mailbox. You can also filter by item type, dates, or keywords. For example:

   # Search a mailbox for all recoverable emails with a certain subject keyword
   Get-RecoverableItems -Identity user@contoso.com -FilterItemType IPM.Note -SubjectContains "Project X"

This command will list all deleted email messages (IPM.Note is the message class for emails) in that user’s Recoverable Items, whose subject contains “Project X”[3]. You can adjust parameters:

• FilterItemType can target other item types (e.g., IPM.Appointment for calendar items, IPM.Contact for contacts, IPM.Task for tasks). If omitted, all item types are returned.

• SubjectContains, SenderContains, RecipientContains can filter by those fields.

• FilterStartTime and FilterEndTime can narrow by deletion timeframe[3].

  Review the output to ensure the desired item(s) are found. The output will show item identifiers needed for restoration.

1. Restore the deleted items: Once you’ve identified items (or if you want to restore everything you found with a given filter), use Restore-RecoverableItems. For example, to restore all items that match the previous search:

   Restore-RecoverableItems -Identity user@contoso.com -SubjectContains "Project X"

This will take all recoverable items in user@contoso.com’s mailbox with “Project X” in the subject and restore them[3]. You can use the same filters as before or specify particular ItemIDs (if you want to restore specific individual items). If not specifying filters, be cautious: running Restore-RecoverableItems without any filter will attempt to restore all deleted items available for that mailbox.

• Target Folder: By default, restored items go to the user’s Deleted Items folder (just like the EAC method)[2]. PowerShell’s restore cmdlet doesn’t let you choose another folder as the destination.

1. Verify the restoration: After running the cmdlet, you can optionally run Get-RecoverableItems again to ensure those items no longer appear (they should be gone once restored), or simply check the user’s mailbox. The user’s Deleted Items folder should now contain the recovered messages or items. You can communicate to the user that the items have been recovered and they will find them in Deleted Items.

PowerShell gives fine-grained control and is especially useful for bulk operations or automation (for example, recovering a particular email for many mailboxes at once, or scheduling regular checks). It requires some expertise, but it’s a robust method when UI tools are insufficient.

3. eDiscovery Content Search (Compliance Center)

If an item is beyond the standard retention period (e.g., older than 30 days and thus not visible in the Recoverable Items folder) but you have configured additional data protection (like a retention policy or Litigation Hold** [3]**), the content might still be recoverable through eDiscovery. Also, if you need to recover a large set of data (for example, all emails from last year for a mailbox), the eDiscovery Content Search is a powerful approach. Microsoft Purview’s Compliance portal allows admins (with eDiscovery permissions) to search and export data from mailboxes.

Steps (Admin eDiscovery Recovery):

1. Go to Microsoft Purview Compliance Center: Visit the compliance portal (https://compliance.microsoft.com) and sign in with an account that has eDiscovery permissions (e.g., Compliance Administrator or eDiscovery Manager roles).

2. Initiate a Content Search: In the Compliance Center, navigate to Content Search (under the eDiscovery section). Create a new search case or use an existing case if one is set up. Then set up a New Search:

   • Name the search (e.g., “Recover John Doe Emails March 2021”).
     

   • Add Conditions/Locations: Specify the location to search – in this case, select Exchange mailboxes and pick the specific user’s mailbox (or multiple mailboxes if needed).
     

   • Set the query for items you want to find. You can filter by keywords, dates, subject, sender/recipient, etc., or even search for all items if you’re attempting a broad recovery. For example, you might search for emails from a certain date range that were lost.

3. Run the search: Start the search and wait for it to complete. Once done, you can preview the results in the portal to verify that the missing/deleted item is found. The search is powerful – it can find items that were permanently deleted by the user but retained for compliance. For instance, if a retention policy holds items for 10 years, an email deleted by the user 6 months ago (and long gone from Recoverable Items) would still show up in this search[4].

4. Export the results: If the needed item is found (or you want all results), use the Export option. When exporting:

   • Choose to export Exchange content as PST file (this is the usual format for mailbox data export).
     

   • The system will prepare the export; you might have to download an eDiscovery Export Tool and use an export key provided in the portal to download the PST to your local machine[4]. Follow the prompts – the portal provides these details.

5. Retrieve data from the PST: Once you have the PST file (Outlook Data File) downloaded, open it with Outlook (by going to File > Open > Open Outlook Data File in Outlook desktop). You’ll then see an additional mailbox/folder set in Outlook corresponding to the exported data. Navigate inside it to find the specific emails or items.

   • You can now copy the needed item back to the user’s mailbox: for example, drag the email from the PST into the user’s Inbox (if you have the mailbox open) or save the item and forward it to the user. If you exported items from only one mailbox and you have access to that mailbox in Outlook, you could also import the PST back into their mailbox directly (with caution to avoid duplicates).
     

   • Another method: instead of you doing this, you could give the PST to the user to review. But usually, the admin or an IT specialist would extract the needed item and restore it to the mailbox.

6. Completion: Given that eDiscovery is a more involved process, you’d likely communicate with the user throughout. After restoring the item, let the user know it has been recovered and where (e.g., restored to their Inbox or sent to them separately).

Note: Content Search requires that the content still exists in the backend (Recoverable Items or Purges or held by a retention policy). If an item was permanently deleted and no hold or retention preserved it, eDiscovery will not find it after the retention period. Also, eDiscovery in Business Premium is available (Content Search is generally included), but features like Litigation Hold or Advanced eDiscovery might require higher licenses. In our scenario, we assume the organization enabled all appropriate data protection (like retention policies) to allow such recovery.

Using eDiscovery is a powerful way for admins to handle “long-term” recovery and is often the only recourse for items that were deleted long ago or when needing to retrieve data from an inactive mailbox.

4. Restoring a Deleted Mailbox (Entire User Mailbox Recovery)

The above methods focus on recovering items within a mailbox. However, what if an entire mailbox was deleted? This can happen if a user account was deleted or their license was removed. In Microsoft 365, when you delete a user, their Exchange Online mailbox is soft-deleted but recoverable for a limited time.

Key point: When a user is removed, the mailbox is retained for 30 days by default (this is separate from item-level retention). Within that 30-day window, an admin can restore the user account and thereby restore the mailbox. After 30 days, the mailbox is permanently deleted (unless it was put on Litigation Hold or converted to an inactive mailbox beforehand, which for Business Premium is not applicable without an upgraded license).

Steps to restore a deleted mailbox/user:

1. Restore the user account: Go to the Microsoft 365 Admin Center > Users > Deleted Users. Find the user who was deleted. Microsoft 365 will list users here for 30 days after deletion.

   • Select the user and choose Restore. You will be prompted to set a new password for the account and (optionally) send sign-in details. Complete the restore process****. This action essentially undeletes the account in Azure AD and reconnects the original mailbox.

2. Reassign licenses: After restoration, ensure the user has the Exchange Online (Business Premium) license assigned (the admin center usually gives an option to reassign the old licenses during restore). The mailbox needs an active license to be accessible. Once restored and licensed, the mailbox will reappear in the Active users list and in Exchange Admin Center as an active mailbox.

3. Verify mailbox content: The mailbox should be exactly as it was at the moment the user was deleted, since it was preserved in soft-delete state. Verify by accessing the mailbox (e.g., via Outlook Web or restoring login to the user). All emails, folders, and other items should be intact. This includes any deleted items that were within retention, etc., as of deletion time. All content is retained during the 30-day soft delete window.

4. Communicate to user or adjust data as needed: If this was a mistake and the user needed to be restored, they can now simply continue using their mailbox. If the goal was to recover some data from a departed user, at this point an admin can access the mailbox to retrieve specific information (or alternatively, you could convert this mailbox to a shared mailbox if the user is not returning, etc., but that’s beyond scope).

If the 30-day window has passed and no holds were in place, the mailbox is permanently removed and cannot be recovered through native means. At that stage, only if a backup exists or if an inactive mailbox was created (requires advanced licensing) could data be retrieved. It’s crucial to act within that window if an entire mailbox (user) needs restoration.

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Additional Notes on Calendar, Contacts, and Tasks Recovery

We touched on this above, but to clarify: emails, calendar items, contacts, and tasks are all treated similarly by Exchange Online’s deletion recovery system.

• When a calendar appointment or meeting is deleted, it goes to Deleted Items (yes, even though it’s not an email, it appears in the Deleted Items folder)[2]. If you permanently delete it from there, it can be recovered from the Recoverable Items folder just like an email. The UI in Outlook makes it appear that only mail is listed, but in reality those appointments are there with a blank sender and the subject line (which is the event title). Once recovered, a calendar item can be dragged back to the Calendar interface to restore it.

• When a contact is deleted, it also lands in Deleted Items (as a contact item). Users can open Deleted Items folder and find the contact (it will show the contact’s name). If it’s not there, recovering via the Recover Deleted Items tool will list the contact by name (with an envelope icon). After recovery, the contact will be in Deleted Items; from there, it can be dragged into the Contacts folder to restore it fully[2].

• When a task is deleted, it behaves in the same way. The task will appear in Deleted Items (and can be restored or dragged back to the Tasks folder). If it was hard-deleted, the Recover Deleted Items tool will show it (again with an envelope icon). After recovering a task, you can drag it from Deleted Items to your Tasks folder.

In summary, all these item types (mail messages, events, contacts, tasks) utilize the same two-stage recycle system (Deleted Items -> Recoverable Items) and thus the recovery methods described for emails apply equally to them[2][2]. The key difference is recognizing them in the recovery interface, since they might not have obvious icons or sender/subject lines like an email. Sorting and carefully reviewing the recovered item list helps identify them.

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Best Practices & Preventative Measures

To minimize data loss and simplify recovery in the future, consider the following best practices and protections in an Exchange Online (Business Premium) environment:

• Extend Deleted Item Retention: Ensure that the mailbox retention for deleted items is set to the maximum if appropriate for your org. By default it’s 14 days, but admins can increase it to 30 days per mailbox. This gives users a larger window to discover and recover deletions on their own, and gives admins more time for recovery as well. In PowerShell, this is done with:

  Set-Mailbox -Identity user@contoso.com -RetainDeletedItemsFor 30

(30 is the max in days). This is especially important for Business Premium, which might not have unlimited archiving – you want to buy as much time as possible for recovery.

• Enable Archive Mailboxes (if available): Microsoft 365 Business Premium now supports archive mailboxes (Online Archive) for users – this was historically an Exchange Plan 2 feature, but Microsoft has made archive available for Business plans as well in recent updates. If not already enabled, admins should enable the Archive Mailbox for each user via EAC or PowerShell. An archive mailbox provides extra storage and can automatically archive old emails (with policies). While it’s not directly a recovery feature, it reduces the likelihood of users deleting stuff just to free up space. Archived mail is still searchable and can be brought back to the main mailbox if needed.

• Use Retention Policies for Compliance: If your organization needs to keep data for longer (for legal or compliance reasons), configure a Microsoft Purview retention policy on mailboxes. For example, you might have a policy “retain all emails for 7 years.” Even on Business Premium, you can create such retention policies (this is a compliance feature available across enterprise plans). With a retention policy, even if a user deletes an item, Exchange will keep a copy in a hidden Recoverable Items subfolder (called the “Preservation Hold” library) for the duration of the policy[4]. This effectively means an admin could recover items long past 30 days via eDiscovery as we showed. Important: Retention policies are different from Litigation Hold, but they serve a similar purpose in preserving data. Make sure to communicate and plan retention policies carefully, since they can also mean mailboxes retain a lot of data invisibly.

• Litigation Hold / In-Place Hold: Business Premium does not include Litigation Hold capability (that’s an Exchange Plan 2 / E3 feature). If long-term hold of all mailbox content is required (for legal reasons), consider upgrading the specific user to an Exchange Online Plan 2 or an E3 license which supports Litigation Hold. Litigation Hold would preserve everything indefinitely (or until hold is removed), making recovery straightforward but it’s a heavier compliance measure. In our scenario “all appropriate protection methods” likely means retention is used since Litigation Hold isn’t available on Business Premium by default.

• Educate and communicate with users: A significant part of data protection is making sure users know how to recover their own items and encouraging good habits:

  • Teach users to check Deleted Items first when they miss something.
    

  • Inform them that if they delete something with Shift+Delete (hard delete), it bypasses Deleted Items but can still be recovered for a period of time with some extra steps[1].
    

  • Encourage users to report missing important emails sooner rather than later, so admins can assist if needed before time runs out.
    

  • If users manage their mailbox via mobile or Mac Mail, etc., ensure they know how deletions work (some clients might immediately hard-delete items). The Outlook web and Windows client both fully support the recovery features as described.

• Implement a Backup Solution (if needed): Microsoft’s retention and recovery features are usually sufficient for most scenarios. However, some organizations opt for a third-party Office 365 backup service that periodically backs up Exchange Online mailboxes. This can protect against catastrophic scenarios or extended delays (e.g., noticing a deletion after a year). While this may be beyond “built-in” methods, it’s worth noting that 3rd-party backups can allow recovery even after Microsoft’s own retention is expired. This is an extra safety net, especially in Business Premium environments where advanced holds aren’t available.

• Monitor mailbox activities: Admins can use audit logs or eDiscovery to monitor unusual deletion activity (for instance, if a user or attacker deletes a large number of items). Early detection can prompt immediate recovery actions. Also, consider enabling alerts for when mailboxes are deleted or retention policies are changed.

By following these best practices, you ensure that “appropriate protection methods” are truly in place and that both users and administrators can collaborate to recover information if something is missing or deleted.

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Conclusion:
In an M365 Business Premium environment, recovering missing or deleted mailbox information is very feasible thanks to built-in Exchange Online features. Users have self-service options for recent deletions, and admins have powerful tools for deeper recovery tasks. The keys to success are understanding the time limits (14/30 days by default, longer if retention policies apply) and acting methodically to retrieve the data. With the detailed processes outlined above, both users and admins can confidently restore emails, calendar events, contacts, or tasks that were thought to be lost.

[3]: Litigation Hold: An advanced mailbox hold feature (not available in Business Premium by default) that preserves all mailbox content indefinitely. If a mailbox were on Litigation Hold, even after 30 days post-deletion, the data would be retained. In such a case, recovery would be done via eDiscovery as well, since the content is held beyond the normal retention. Business Premium tenants may need an upgrade for this, so retention policies are the alternative.

References: The information above was compiled from Microsoft documentation and community content, including Microsoft Learn guides on recovering deleted mailbox items[3][3], Microsoft Support articles on Outlook item recovery[2][2], and Exchange Online blog and community posts detailing retention and recovery behaviors[1][4]. Each specific detail is backed by these sources to ensure accuracy.

References

[1] Restore Hard-Deleted Emails in Exchange Online

[2] Recover and restore deleted items in Outlook – Microsoft Support

[3] Recover deleted messages in a user’s mailbox in Exchange Online

[4] Recoverable items in Exchange online. – Microsoft Community