How to Import PST to Office 365 Shared Mailbox (2026 Guide)

Consolidating departmental email history into a Microsoft 365 Shared Mailbox (such as info@company.com or support@company.com) allows teams to access centralized customer correspondence and historical communications.

Because Exchange Online shared mailboxes do not require a paid standalone license as long as storage remains under 50 GB, importing historical PST files into shared mailboxes is an effective strategy for retiring legacy workstations while preserving organizational knowledge.

Shared Mailbox Storage and Licensing Rules

Understanding Microsoft's licensing constraints prevents import failures:

Administrative Prerequisites for Shared Mailbox Import

Before starting an import job, configure administrative access:

1. Assign Delegated Mailbox Permissions:

In the Microsoft 365 admin center, navigate to Teams & groups > Shared mailboxes. Select the mailbox, click Members, and add your administrative account under Read and manage permissions. Allow up to 60 minutes for permission propagation.

2. Assign Purview Import Roles (For AzCopy Imports):

If performing a server-side network upload, ensure your administrator account has the Mailbox Import Export role assigned within the Exchange Admin Center (Roles > Admin roles > Organization Management).

Method 1: Client-Side Import via Classic Outlook Desktop

For smaller PST archives under 5 GB, Classic Outlook provides a straightforward import method via delegated profile mapping.

┌────────────────────────────────────────────────────────┐
│  CLASSIC OUTLOOK SHARED MAILBOX IMPORT FLOW            │
├────────────────────────────────────────────────────────┤
│  1. Delegate Access: Admin assigned "Read and manage"  │
│  2. Auto-Discovery: Shared Mailbox renders in Outlook  │
│  3. Import Wizard: File > Open & Export > Import/Export│
│  4. Target: Select Shared Mailbox destination folder   │
│  5. Background Sync: Uploads items via MAPI/HTTP       │
└────────────────────────────────────────────────────────┘

Step-by-Step Procedure

1. Open Microsoft Outlook (Classic) signed in as the authorized administrator.
2. Verify that the target shared mailbox appears in your left-hand folder tree below your primary mailbox.
3. Click File > Open & Export > Import/Export.
4. Select Import from another program or file and click Next.
5. Select Outlook Data File (.pst) and click Next.
6. Browse to select your local .pst file and specify your duplicate handling preference.
7. Select Import items into the current folder or Import items into the same folder in: and select the shared mailbox root.
8. Click Finish and keep Outlook running until client synchronization completes.

Method 2: Enterprise Network Upload via Microsoft Purview (AzCopy)

For large departmental archives, Microsoft's official PST Import Service provides a resilient server-side pipeline.

Step 1: Generate Azure Storage SAS URL

1. Sign in to the Microsoft Purview portal (purview.microsoft.com) or compliance portal (compliance.microsoft.com).
2. Navigate to Data lifecycle management > Microsoft 365 > Import.
3. Click New import job, provide a descriptive job name, and click Next.
4. Select Upload your data and click Show network upload SAS URL. Copy the URL to your clipboard.

Step 2: Upload Files via AzCopy

Open Windows PowerShell and use the official Microsoft AzCopy tool to stream local PST files to the Azure staging container:

.\azcopy.exe copy "C:\PSTFiles\" "<Azure-SAS-URL>" --recursive=true

Step 3: Create the Mapping CSV

Create a mapping file named PstImportMapping.csv specifying the target shared mailbox SMTP address:

WorksheetName,FilePath,Name,Mailbox,IsArchive,TargetRootFolder,ContentCodePage,SPFileContainer,SPManifestContainer,SPSiteUrl
PSTMapping,,SalesDept.pst,sales@company.com,FALSE,/,1252,,,,
PSTMapping,,SupportDept.pst,support@company.com,FALSE,/PST_Archive/,1252,,,,

Step 4: Validate and Run the Job

Return to the Purview Import wizard, upload your CSV file, click Validate, and save the job once validation completes. The Mailbox Replication Service (MRS) processes the import asynchronously in the cloud.

Method 3: Pre-Migration Inspection & Staging via Prism PST Converter

When dealing with legacy PST files that have structural damage, password locks, or unknown contents, uploading them directly through AzCopy can result in corrupted item failures.

Using Prism PST Converter Tool allows administrators to inspect and prepare PST data before uploading:

1. Launch Prism PST Converter Tool on your workstation.
2. Click Add File or Add Folder to mount the PST files.
3. Review message bodies, attachments, and folder hierarchies in the interactive preview pane.
4. Filter out unneeded folders (such as Deleted Items or Junk) to keep the archive well within the 50 GB free shared mailbox threshold.
5. Export sanitized, healthy PST files ready for Purview ingestion or local record keeping.

Technical Comparison of Methods

Frequently Asked Questions (FAQs)

Do I need a paid license to import PST files into a Shared Mailbox?

No. An Exchange Online Shared Mailbox is included without additional license cost as long as its total mailbox storage does not exceed 50 GB. If your data exceeds 50 GB, an Exchange Online Plan 2 license must be assigned.

Can multiple team members access the imported emails simultaneously?

Yes. Once imported into the shared mailbox, all users assigned Read and manage (Full Access) permissions can view, search, and organize messages concurrently across Outlook Desktop, Outlook on the Web, and mobile clients.

How do I grant team members access to the Shared Mailbox after import?

In the Microsoft 365 admin center, go to Teams & groups > Shared mailboxes, select the mailbox, and add user accounts under the Members section with Read and manage and optionally Send As permissions.

What happens if an imported PST file exceeds the 50 GB limit?

If an unlicensed shared mailbox reaches 50 GB, Exchange Online stops accepting new email and halts active import operations. Administrators must assign an Exchange Online Plan 2 license to increase the quota to 100 GB.

Summary

Importing historical PST archives into Microsoft 365 Shared Mailboxes consolidates team correspondence while minimizing recurring licensing costs. For small archives under 5 GB, Classic Outlook's built-in import wizard provides an accessible client workflow. For enterprise-scale archives, the Microsoft Purview Network Upload pipeline using AzCopy and CSV mapping ensures centralized processing. When legacy files are damaged or require quota filtering, preparing data with Prism PST Converter Tool ensures a reliable migration.

Related Guides:

• How to Import PST to Office 365 Online Archive
• How to Export Office 365 Mailbox to PST via PowerShell