How do I import a PST into a mailbox?

You can import a PST file into a mailbox either directly in the Outlook desktop app or, in Microsoft 365, by using admin‑level import methods for user or archive mailboxes. Choosing the right method depends on whether you are moving data for a single user, multiple users, or into an online archive.​

What importing a PST actually does

A PST (Outlook Data File) stores mailbox items such as emails, calendar entries, contacts, tasks, and notes that can be merged into an existing mailbox or opened as a separate data file. When you import a PST, Outlook, or Microsoft 365 reads the file and copies its contents into a target mailbox folder structure while preserving item properties like subject, sender, and timestamps.​

Common scenarios for PST import

Users typically need PST import when moving from an old PC or Outlook profile, recovering data from a backup, or consolidating multiple PST archives into one mailbox. In organizations, admins often import multiple PST files into Microsoft 365 mailboxes during migration projects or when bringing legacy archives into online archive mailboxes.​

Method 1: Import PST into Outlook desktop

For an individual mailbox, the simplest method is to import the PST using the Outlook Import/Export wizard. In classic Outlook for Windows, you go to File> Open & Export> Import/Export, choose "Import from another program or file," pick "Outlook Data File (.pst)," browse to the PST, and select whether to import into the current mailbox and include subfolders. You can import into the main mailbox root or a specific folder so that data integrates neatly without overwriting existing content.​

Method 2: Open PST as a data file

Instead of merging content, you can attach the PST as a separate data file to keep old emails logically isolated. Using File> Open & Export> Open Outlook Data File, you select the PST, and Outlook mounts it as an additional tree in the folder pane, allowing you to drag and drop items into the live mailbox only when needed. This approach is ideal when you want read‑only access to legacy data while controlling exactly what you copy into the active mailbox.​

Method 3: Import PST into Microsoft 365 mailbox

If the mailbox is hosted in Microsoft 365 but you have Outlook desktop, you can still import the PST using Outlook; the data syncs up to the cloud mailbox over time. For larger projects or when you do not want to rely on local Outlook clients, Microsoft 365 provides tenant‑level import options that let admins upload PSTs directly into user mailboxes or archive mailboxes.​

Bulk import using network upload

For organizations, the network upload method lets you copy PST files to Microsoft 365 and map each file to a target mailbox. The high‑level flow is: assign the Mailbox Import Export role, use the AzCopy tool to upload PSTs to an Azure storage location, create an import job in the compliance portal, and submit a CSV mapping file that links each PST to the appropriate user or archive mailbox. Once the job runs, Microsoft 365 ingests the PST content directly into the specified mailboxes without manual intervention on user machines.​

PowerShell and admin‑driven imports

In hybrid or on‑premises Exchange environments, admins can use PowerShell cmdlets such as New‑MailboxImportRequest to import PST files from a file share into user mailboxes or archives. This method requires the Mailbox Import Export role, access to the network path hosting the PST, and careful selection of the target root folder where imported items should appear. Admin‑driven imports allow better control, automation, and monitoring of bulk PST migrations than user‑initiated Outlook imports.​

Best practices before importing

Before importing, always check that the PST is healthy and not corrupted, ideally by opening it in Outlook or using repair tools if necessary. Plan folder mappings to avoid duplicate structures, verify mailbox quotas so the import does not exceed storage limits, and consider importing into an archive mailbox if users have large historical data sets.​

Tips to optimize for a smooth import

To keep performance stable, avoid importing very large PSTs during peak working hours and consider splitting extremely large archives into smaller files. Document which PSTs were imported, where they were placed, and communicate clearly with end users so they know where to find their restored folders and how to manage them after the import completes.​

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