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PST Office 365

Convert PST to Office 365
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Learn how to import PST files into Office 365 (Microsoft 365). Step-by-step guide covering Network Upload, drive shipping, and third-party tools like MailtoPst.

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What is a PST file?

PST (Personal Storage Table) is the file format used by Microsoft Outlook to store emails, contacts, calendar entries, and tasks locally on your computer. When organizations migrate to the cloud, PST files are often the primary data source that needs to be imported into Office 365 mailboxes.

PST files accumulate over years of Outlook usage and can grow to dozens of gigabytes. They contain:
- Email messages with full headers, body, and attachments
- Folder hierarchy — Inbox, Sent Items, custom folders, and subfolders
- Calendar data — appointments, meetings, and recurring events
- Contacts and distribution lists — your entire address book
- Tasks and notes — productivity items stored in Outlook

Importing PST data into Office 365 is one of the most common migration tasks for IT administrators and end users moving to Microsoft's cloud platform.

What is a Office 365 file?

Office 365 (now Microsoft 365) is Microsoft's cloud-based productivity suite that includes Exchange Online for email hosting. When you import PST files into Office 365, emails are uploaded to cloud-hosted mailboxes accessible from Outlook desktop, Outlook Web App, and mobile devices.

Key benefits of migrating PST to Office 365:
- Cloud accessibility — access your emails from any device, anywhere
- Centralized management — IT admins can manage all mailboxes from one admin center
- Built-in compliance — litigation hold, eDiscovery, and retention policies
- Automatic backups — Microsoft handles data redundancy and disaster recovery
- Scalable storage — 50 GB to 100 GB per mailbox depending on your plan

Office 365 supports direct PST import through several methods, including the Microsoft Import Service in the Security & Compliance Center.

Why convert PST to Office 365?

Migrating PST files to Office 365 is essential for organizations modernizing their email infrastructure:

1. Cloud-first strategy
Moving from local PST files to Office 365 eliminates the risks of local data storage — hardware failures, theft, and lack of centralized backups. Your email data is stored securely in Microsoft's data centers with geo-redundancy.

2. Compliance and legal requirements
PST files scattered across employee laptops are a compliance nightmare. Importing them into Office 365 enables centralized eDiscovery, litigation holds, and retention policies required by regulations like GDPR, HIPAA, and SOX.

3. Decommissioning on-premises Exchange
When migrating from Exchange Server to Exchange Online, PST files from former employees or archived mailboxes need to be imported into the cloud to maintain complete email records.

4. User onboarding
New employees joining from other organizations often bring PST exports of their professional email history. Importing these into Office 365 ensures continuity and access to historical communications.

PST vs Office 365 — Key Differences

Feature PST Office 365
Storage location Local file on disk Microsoft cloud (Exchange Online)
Accessibility Single device only Any device, anywhere
Backup Manual (user responsibility) Automatic (Microsoft managed)
Compliance tools None built-in eDiscovery, retention, litigation hold
Max size Up to 50 GB (Outlook limit) 50-100 GB per mailbox
Search Local Outlook index Cloud-powered instant search

3 methods to convert PST to Office 365

Method 1: Microsoft 365 Import Service (Network Upload)

Use the Import Service in the Microsoft Purview compliance portal to upload PST files via Azure AzCopy. This is the official method for bulk imports. Requires admin access and a CSV mapping file.

Pros

  • ✓ Official Microsoft method
  • ✓ Free (included in subscription)
  • ✓ Handles large volumes

Cons

  • ✗ Requires Global Admin role
  • ✗ Complex CSV mapping file needed
  • ✗ AzCopy command-line tool required
  • ✗ Slow for large datasets (days/weeks)

Method 2: Outlook desktop import

Open the PST file in Outlook connected to Office 365, then drag-and-drop or use File > Open & Export > Import to move emails into your cloud mailbox.

Pros

  • ✓ Simple for end users
  • ✓ No admin access needed
  • ✓ Familiar Outlook interface

Cons

  • ✗ Very slow for large PST files
  • ✗ Requires Outlook desktop installed
  • ✗ Not suitable for bulk migration
  • ✗ May time out on large files
Recommended

Method 3: Convert with MailtoPst then import

Use MailtoPst to convert your PST to EML or MBOX format, then import the converted files into Office 365. This approach works from any browser without Outlook installed and is ideal when you need to restructure or filter emails before importing.

Pros

  • ✓ No Outlook needed for conversion
  • ✓ Works on Mac, Linux, Windows
  • ✓ Filter and preview emails before import
  • ✓ GDPR compliant, EU servers

Cons

  • ✗ Two-step process (convert then import)
  • ✗ Requires internet connection
  • ✗ Paid after first conversion
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Step by step

How to convert PST to Office 365 with MailtoPst

01

Upload your PST file

Drag & drop or click to upload your .pst file. Files up to 51 GB supported with resumable upload.

02

Choose Office 365 as output

Select Office 365 from the format dropdown. MailtoPst auto-detects the best conversion settings.

03

Download your Office 365 file

Conversion takes seconds. Download your .office365 file or receive it by email.

Convert your PST to Office 365 now →

100 MB free credit. No credit card required.

FAQ

Frequently Asked Questions

Can I import PST to Office 365 without admin access?

Yes. As an end user, you can open the PST file in Outlook desktop connected to your Office 365 account and manually import or drag emails into your cloud mailbox. Alternatively, use MailtoPst to convert the PST to EML files you can upload via Outlook Web App.

How long does a PST to Office 365 migration take?

It depends on the method and file size. The Microsoft Import Service processes about 24 GB per day via Network Upload. Outlook desktop drag-and-drop is much slower. For a 10 GB PST, expect 1-3 days via Import Service, or several hours via Outlook.

Is there a size limit for PST import to Office 365?

Microsoft recommends PST files be no larger than 20 GB for optimal Network Upload performance. There is no hard limit, but larger files take exponentially longer and may fail. MailtoPst supports PST files up to 50 GB.

Will folder structure be preserved when importing PST to Office 365?

Yes. Both the Microsoft Import Service and Outlook desktop import preserve the original PST folder hierarchy. Custom folders, subfolders, and their contents are mapped to corresponding folders in your Office 365 mailbox.

Can I import PST to Office 365 from a Mac?

The Microsoft Import Service works from any OS via a web browser, but requires admin access. For end users on Mac, the easiest approach is to convert the PST to EML or MBOX with MailtoPst, then import using Outlook for Mac or Outlook Web App.

Related conversions

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