How to Import a PST File to Office 365

The Problem: Moving PST Files Into the Cloud

Microsoft 365 (formerly Office 365) stores email in Exchange Online mailboxes rather than in local PST files. If you are migrating from an on-premises Outlook installation to Microsoft 365, or if you have archived PST files that need to be accessible in the cloud, you need a way to get those PST contents into your Exchange Online mailbox.

The challenge is that Microsoft’s built-in import tools require admin access or Azure infrastructure, which puts them out of reach for individual users. For IT administrators handling bulk migrations, the process involves network uploads to Azure Blob Storage or physical drive shipments — neither is simple for a quick one-off import.

Solution: Import PST to Office 365

There are several approaches depending on your role and the volume of data.

Method 1: Microsoft 365 Import Service (Admin Required)

Microsoft provides a PST Import Service within the Microsoft 365 compliance center. This is the official method but requires global admin or mailbox import/export role permissions.

1. Access the compliance center at compliance.microsoft.com and navigate to Information governance, then Import.
2. Create a new import job and choose either “Upload over the network” or “Ship a hard drive.”
3. For network upload — download the Azure AzCopy tool, copy the SAS URL provided, and upload your PST files to the Azure Blob Storage location.
4. Create a mapping CSV — specify which PST files map to which user mailboxes, and whether to import into the primary mailbox or an archive mailbox.
5. Validate and start the import job. Microsoft processes the files and imports them into the target mailboxes.

This method handles large-scale migrations (hundreds of PST files) but requires significant setup.

Method 2: Outlook Desktop Import (Individual Users)

If you have the Outlook desktop application connected to your Microsoft 365 account, you can import a PST file directly.

1. Open Outlook and ensure it is connected to your Microsoft 365 mailbox.
2. Go to File, then Open & Export, then Import/Export.
3. Select “Import from another program or file” and choose Outlook Data File (.pst).
4. Browse to your PST file and choose whether to replace duplicates, allow duplicates, or skip duplicates.
5. Select the folders to import and the destination mailbox.
6. Outlook syncs the imported messages to Exchange Online automatically.

This works well for individual files but becomes impractical for large archives or batch migrations.

Method 3: Convert PST First, Then Upload Selectively

For users who want more control or do not have admin access to Microsoft 365 import tools, converting the PST into individual EML files allows selective upload.

1. Convert PST to EML on mailtopst.com — each message becomes a standalone file.
2. Open Outlook (desktop or web) connected to your Microsoft 365 account.
3. Drag EML files into the appropriate Outlook folder. Outlook accepts EML files as drag-and-drop imports.

This approach is ideal when you only need specific messages from a large archive, or when the PST file needs to be split across multiple mailboxes.

Why MailtoPst Helps With Office 365 Migration

• Pre-conversion flexibility — convert PST to EML or MBOX before uploading, giving you control over what goes into your mailbox.
• No admin access needed — individual users can handle the migration themselves.
• File integrity — attachments, dates, headers, and folder structure are preserved during conversion.
• Secure handling — files are encrypted via TLS, processed on EU servers, and auto-deleted after conversion. GDPR compliant throughout.
• Large file support — handles PST files up to 50 GB, matching Microsoft’s own PST size recommendations.

Try free — no credit card required. Get 100 MB of free conversion credit to test the process.

Tips for a Successful Import

• Check mailbox quotas — Microsoft 365 plans have storage limits (50 GB or 100 GB depending on the plan). Verify available space before importing large PST files.
• Use archive mailboxes — if your organization has enabled archive mailboxes, import older emails there to keep the primary mailbox lean.
• Remove duplicates — if the PST contains messages already in your mailbox, use the “do not import duplicates” option.
• Test with a small file first — before importing a 20 GB PST, test the process with a few hundred messages to confirm everything works correctly.

Frequently Asked Questions

Can I import a PST file into Outlook on the web (OWA)?

Outlook on the web does not have a built-in PST import feature. You need either the Outlook desktop client or the Microsoft 365 admin import service. Alternatively, convert the PST to EML files with MailtoPst and drag them into OWA.

Do I need admin access to import PST into Microsoft 365?

For the official Microsoft Import Service, yes — you need global admin or the mailbox import/export role. For importing via the Outlook desktop client, no admin access is required as long as Outlook is connected to your Microsoft 365 account.

Will the folder structure be preserved?

Yes. When using Outlook’s built-in import, the original folder structure from the PST is recreated in your mailbox. When importing EML files manually, you need to create the folder structure yourself.

How large can a PST file be for import?

Microsoft recommends keeping PST files under 20 GB for the import service, though technically larger files work. MailtoPst can convert files up to 50 GB if you need to split or restructure before import.

Can I import PST files from a non-Microsoft email client?

If you have PST files generated by a third-party tool, they should follow the same MS-PST specification. MailtoPst reads any standard PST file regardless of which application created it.

Upload your file now and simplify your migration to Microsoft 365.