If you’re responsible for a Microsoft 365 migration, moving PST files is rarely just a matter of uploading a few files and waiting for them to finish.

The real challenge starts when you have multiple PST files, multiple users, different file locations, and specific Microsoft 365 mailboxes that each file needs to reach.

Microsoft provides a native PST Import service for administrators, while dedicated migration software can offer another way to organize and manage a larger PST migration.

In this guide, we’ll explain how to import PST to Office 365, what Microsoft’s native method involves, when a different migration approach may make sense, and what to check before moving your organization’s Outlook data.

Contents

How to Import PST to Office 365

The best method depends on how much PST data you have and how you need to manage the migration.

For an organization-wide migration, Microsoft 365 provides a native PST Import service through the Microsoft Purview portal. With the network-upload method, administrators upload PST files to Microsoft-managed Azure Storage using AzCopy, create a CSV mapping file that associates each PST with a Microsoft 365 mailbox, create an import job, and then start the import. Microsoft also provides a drive-shipping option.

For smaller migrations, a manual Outlook-based approach may be enough. For larger or more structured projects, administrators may also evaluate a dedicated PST to Office 365 migration tool.

The right choice usually comes down to:

How many PST files need to be migrated
How many Microsoft 365 mailboxes are involved
Where the PST files are stored
How the PST files need to be mapped
Whether the migration is a one-time job or requires additional passes
How much monitoring and reporting the IT team needs
What administrative resources are available

Why Do Organizations Import PST Files into Microsoft 365?

PST files often contain years of Outlook data.

Employees may have created PST files to archive older email, move data between computers, or keep local copies of historical messages. Over time, an organization can end up with PST files spread across employee computers, file servers, shared folders, and other storage locations.

When an organization moves to Microsoft 365, those files can become a migration problem.

Instead of asking users to keep searching through old PST archives, an administrator may want to bring relevant historical data into Microsoft 365 mailboxes.

Microsoft describes PST import as a way to bring an organization’s archival messaging data into Microsoft 365 so that users can access the data from their devices.

For an IT administrator, the goal is straightforward:

Move the right Outlook data to the right Microsoft 365 mailbox and keep the migration under control.

When Should You Import PST to Office 365?

There isn’t one reason to migrate PST files. The requirement usually appears as part of a broader Microsoft 365 or Outlook data-management project.

Moving an organization to Microsoft 365: If users have historical email stored in PST files, those files may need to be considered as part of the move to Microsoft 365.
Consolidating old Outlook archives: Employees may have accumulated multiple PST files over the years. Importing relevant data into Microsoft 365 can help reduce dependence on scattered local archives.
Migrating data from employee computers: If PST files are stored on individual workstations, collecting and mapping them becomes an administrative task during a migration.
Managing a multi-user migration: When dozens of PST files need to be associated with different Microsoft 365 mailboxes, a structured mapping process becomes increasingly important.
Completing a historical mailbox migration: Some organizations move current mailbox data first and then deal with historical PST archives separately.

In each case, the administrator needs to consider not only how to import PST, but also where the imported data should go and how the migration will be verified.

What Makes PST to Office 365 Migration Difficult?

A single PST file is one thing. A migration involving hundreds of files is another.

Here are some of the issues administrators commonly need to deal with.

PST Files May Be Scattered Across Different Locations

You may find PST files on:

Employee computers
Local drives
File servers
Network shares
Shared storage
Archived systems

Before migration starts, someone needs to identify which files are actually required and which user or mailbox each file belongs to.

Mailbox Mapping Needs to Be Accurate

Suppose you have:

john.pst
mary.pst
sales-archive.pst

Each file may have a different Microsoft 365 destination.

A migration process therefore needs a clear relationship between the source PST and target mailbox.

Microsoft’s PST Import service uses a CSV mapping file for this purpose. The mapping can specify the destination mailbox and whether the PST should be imported into the primary mailbox or archive mailbox.

Manual Migration Gets Repetitive

Opening PST files individually may work for a small task. It becomes much harder to manage when the administrator has to repeat the same process for many users.

The larger the project, the more useful it becomes to have a repeatable migration workflow.

You Need to Know What Happened

During a migration, the administrator may need answers to simple questions:

Which PST files are finished?
Which ones are still processing?
Did a particular mailbox receive its data?
Were any files skipped or rejected?
Does anything need to be migrated again?

Migration visibility becomes particularly important when the project has a deadline.

What Should You Check Before You Import PST to Office 365?

A little preparation can prevent a lot of troubleshooting later.

1. Inventory the PST Files

Start by creating a list of the PST files you intend to migrate.

At minimum, record:

Information	Example
PST file	John-Archive.pst
User	John Smith
Source location	\\Server\PSTs
Target mailbox	john@company.com
Destination	Primary or archive mailbox
Migration status	Pending

The exact fields you need will depend on your migration process.

2. Verify the Target Mailboxes

Make sure the destination Microsoft 365 mailboxes exist and that each PST has a known destination.

This is particularly important when many users are involved.

3. Check Microsoft 365 Permissions

Microsoft’s current documentation identifies required permissions for accessing and creating PST import jobs, including the relevant Exchange Online roles. Microsoft recommends using the least-privileged permissions necessary rather than automatically using Global Administrator access.

4. Review PST Size and Import Requirements

Microsoft’s current network-upload guidance states that individual PST files should not be larger than 20 GB, as larger files may affect import performance. Microsoft also documents other PST import limits and requirements that should be reviewed before a production migration.

5. Keep the Original PST Files

Don’t delete the source PST files immediately after the migration appears to complete.

First verify the destination data and follow your organization’s retention and disposal policies.

Method 1: Import PST to Office 365 Using Microsoft’s Import Service

For administrators handling organizational PST files, Microsoft’s native Import service is the most direct Microsoft-provided approach.

The current network-upload workflow is:

Open the Microsoft Purview portal.
Create a PST import job.
Obtain the organization’s SAS URL.
Download the supported version of AzCopy.
Upload the PST files to Microsoft’s Azure Storage location.
Create the PST Import mapping CSV.
Validate the mapping file.
Create the import job.
Analyze or filter the PST data if required.
Start the import.

Microsoft’s current documentation describes these steps for bulk-importing multiple PST files into Microsoft 365 mailboxes.

Step 1: Create a PST Import Job

Create a new import job and choose the option to upload your data.

Microsoft’s Import service then provides the information required for the network-upload process.

Step 2: Get the SAS URL and AzCopy

The network-upload method uses AzCopy to upload the PST files to a Microsoft-provided Azure Storage location.

Microsoft provides the required AzCopy download from the Import workflow. The SAS URL contains access information for the organization’s upload location, so Microsoft recommends protecting it like other sensitive security information.

This is an important detail to keep in mind if multiple administrators are working on the migration.

Step 3: Upload the PST Files

Once AzCopy is available, upload the PST files to the Azure Storage location provided by Microsoft.

The PST files must be available from a supported source location, such as a file share or file server in the organization. Microsoft notes that the Azure Storage location used for this process is in the same regional Microsoft datacenter as the organization.

For a large migration, it makes sense to organize the source files before uploading them.

Step 4: Create the PST Import Mapping File

This is one of the most important parts of the process.

The mapping CSV tells Microsoft 365 which PST belongs to which mailbox.

For example:

PST	Microsoft 365 destination
John.pst	john@company.com
Mary.pst	mary@company.com
SalesArchive.pst	sales-user@company.com

Microsoft’s mapping file supports additional parameters, including whether the destination is a user’s primary or archive mailbox.

Pay attention to filenames and paths. Microsoft notes that values such as PST filenames and optional folder paths are case-sensitive in the mapping process.

For larger migrations, this mapping file is effectively the bridge between your source data and your Microsoft 365 mailboxes.

Step 5: Validate the Mapping File

Upload the CSV to the Microsoft 365 Import service and validate it.

If validation fails, Microsoft provides an error report that identifies the rows that need attention. The mapping file must pass validation before the import job can be created.

This is a good place to catch problems before they affect the actual migration.

Step 6: Analyze and Filter the PST Data

Microsoft 365 can analyze the PST data after the import job is created.

Microsoft’s current Intelligent Import feature can identify information such as the age of mailbox items and message types, allowing administrators to apply filters before importing the data.

This can be useful when the organization doesn’t need every item stored in every PST.

Step 7: Start the Import

Once the configuration is ready, start the PST import.

Microsoft 365 uses the mapping information to import the PST files into the specified mailboxes, and the Import page provides status information about the job and individual PST files.

After the job finishes, verify the destination mailboxes before considering the migration complete.

Method 2: Manually Move PST Data Using Outlook

For a small, one-off migration, an administrator may choose to open a PST in Outlook and move or copy its contents into the appropriate Microsoft 365 mailbox.

This can be reasonable when you’re dealing with one or two files.

But consider what happens when the task becomes:

50 PST files → 50 users → 50 mailboxes

The process becomes repetitive, and the administrator has more opportunities to make mapping or tracking mistakes.

Manual Outlook operations can therefore be better suited to limited, individual migrations than large-scale administrative projects.

Method 3: Use a PST to Office 365 Migration Tool

A dedicated migration application is another option when the project requires a more structured workflow.

This can be particularly relevant when an administrator needs to manage:

Multiple PST or OST files
Multiple users
Mailbox mapping
Bulk migration
Concurrent migration
Incremental or delta migration
Migration progress
Migration logs and reports

The supplied Stellar product persona specifically identifies these needs for the Microsoft 365 / Outlook Administrator and positions Stellar Migrator for Outlook around PST/OST migration to Microsoft 365 and supported Exchange environments.

How Stellar Migrator for Outlook Fits a Microsoft 365 Migration

Stellar Migrator for Outlook is positioned for administrators and migration professionals who need to move Outlook PST/OST data to Microsoft 365 or supported Exchange destinations.

The important point isn’t simply that the software can migrate PST data.

For an administrator, the bigger question is:

Can I manage the migration from source files to the correct Microsoft 365 mailboxes without turning the project into a series of manual tasks?

The supplied product persona identifies several capabilities that address this workflow.

How to Import PST to Office 365: A Practical Guide for Microsoft 365 Administrators

Mailbox Mapping

Mailbox mapping connects the source Outlook data with the intended Microsoft 365 destination.

The product positioning includes automatic or custom mailbox mapping and CSV-based mapping.

This is particularly relevant when an administrator is migrating data for many users.

Bulk and Concurrent Migration

When multiple users are involved, processing every PST individually can increase migration time and administrative effort.

The supplied product information identifies bulk and concurrent migration as part of the product’s migration capabilities.

This makes the capability relevant to larger migration projects where multiple mailboxes need to be handled as part of one overall workflow.

Incremental or Delta Migration

Not every migration ends after the first pass.

If new or changed data needs to be migrated after an initial transfer, an incremental or delta migration workflow can be useful.

Stellar’s supplied product persona identifies incremental/delta migration as one of the capabilities relevant to the administrator persona.

The exact behavior should be verified against the current product version and migration scenario before deployment.

Migration Progress and Monitoring

An administrator shouldn’t have to guess whether a migration is still running.

The supplied product positioning includes migration monitoring and progress visibility.

For a multi-user migration, this can help the IT team understand what has completed and where attention may be required.

Logs and Reports

Migration projects often need documentation.

The supplied product persona identifies migration logs and reports among the buying criteria for administrators and migration professionals.

These can be useful when reviewing migration activity or documenting the outcome of a project.

Final Thoughts

For an administrator, importing PST to Office 365 is not just a file-transfer task. The bigger challenge is organizing the source data, mapping it to the right Microsoft 365 mailboxes, executing the migration, monitoring progress, and verifying the result.

Microsoft’s native Import service provides a structured way to bulk-import organizational PST files. The network-upload workflow uses AzCopy, Azure Storage, a mapping CSV, Microsoft Purview, and an import job.

For more involved migration projects, a dedicated PST migration tool can be another option to evaluate.

Stellar Migrator for Outlook is positioned for Microsoft 365 and Outlook administrators who need to manage PST/OST migration with capabilities such as mailbox mapping, bulk/concurrent migration, incremental/delta migration, progress monitoring, and migration reporting.

The right approach depends on your environment, the number of PST files and mailboxes, the migration workflow you need, and the level of control your IT team wants.

If you’re planning a multi-user migration, start with the migration requirements—not the tool. Once you know how the data needs to move, it’s much easier to choose the right way to import PST to Office 365.

FAQs

Can I import PST to Office 365?

Yes. Microsoft provides a native PST Import service for importing organizational PST files into Microsoft 365 mailboxes. The network-upload method uses AzCopy, Microsoft-managed Azure Storage, a PST mapping CSV, and an import job.

What is the easiest way to import PST to Microsoft 365?

For an organization-wide migration, Microsoft’s native Import service is the official administrative option. For more structured migration projects, a dedicated PST migration tool may be worth evaluating based on requirements such as mailbox mapping, bulk migration, monitoring, and incremental migration.

Can I import multiple PST files into Office 365?

Yes. Microsoft’s network-upload method is designed to bulk-import multiple PST files into Microsoft 365 mailboxes.

Can I map PST files to specific Microsoft 365 mailboxes?

Yes. Microsoft uses a PST Import mapping CSV to associate each PST with its destination mailbox. The mapping can also specify whether the data goes to a primary or archive mailbox.

Can I import PST directly into an archive mailbox?

Yes. Microsoft’s PST Import mapping supports importing a PST into a user’s archive mailbox.

Do I need Outlook to import PST files into Microsoft 365?

You don’t need to manually open each PST in Outlook when using Microsoft’s organizational PST Import service. The network-upload workflow uses AzCopy and the Microsoft 365 Import service.

Do I need AzCopy to import PST files using Microsoft’s network-upload method?

Yes. Microsoft currently specifies AzCopy as the supported tool for uploading PST files through the network-upload workflow. Microsoft also states that Azure Storage Explorer isn’t supported for directly uploading PST files to the Microsoft 365 Azure Storage area.

Can I filter PST data before importing it?

Yes. Microsoft’s current Intelligent Import capability can analyze PST data and provide filtering options before the data is imported into the target mailboxes.

What permissions are required to import PST to Microsoft 365?

The exact permissions depend on the Microsoft 365 import workflow. Microsoft documents the required roles for accessing and using the PST Import service and recommends using the least-privileged permissions necessary.

Should I delete the original PST files after migration?

Not immediately. First verify that the required data has reached the destination and follow your organization’s retention and data-disposal policies.

Is a PST migration tool better than Microsoft’s Import service?

Not necessarily. Microsoft’s Import service is the native Microsoft 365 approach. A dedicated migration tool may be more appropriate for a project that needs additional migration management capabilities. Compare the options against your actual requirements rather than assuming one method is universally better.

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