How to Export an Office 365 Mailbox to PST: Purview, Outlook and Backup Tool Compared

A leaver's mailbox needs to be kept. Legal wants a copy of three people's mail. Or you want an offline backup that does not depend on Microsoft. All three end in the same place: an Outlook Data File. Office 365 gives you two built-in routes to export Office 365 mailbox to PST and neither is obvious. This guide walks through the Purview eDiscovery export as it works after the 2025 change, the Outlook wizard for a single mailbox and the backup tool route for doing it for everyone, every week.

Before You Export an Office 365 Mailbox to PST

• Time1 to 3 hours
• DifficultyMedium
• CostIncluded in E3/E5
• Runs onBrowser + Windows

Who needs the PST and how often? That picks the route, so choose the card that fits.

Export an Office 365 Mailbox to PST with Purview eDiscovery in 6 Steps

This is the admin route and the one that changed in 2025. The old flow of Content Search, Export results, eDiscovery Export Tool is gone. Everything now runs inside a case, and the export downloads as ZIP packages.

1Step 1Open Purview eDiscovery and create a case

Using an eDiscovery Manager account, sign in at purview.microsoft.com and open eDiscovery, then Cases, and click Create case. Name it for the request, such as the leaver's name and the month. A case is a container for the searches, holds and exports that belong to one job.

2Step 2Add the mailbox and its archive as data sources

Inside the case open Data sources and click Add data sources. Search for the user and tick both Mailbox and Archive mailbox (the In-Place Archive). Leave OneDrive off unless the request covers files. An Office 365 mailbox and its archive are separate sources, so a missed tick here means missing years later. For a leaver whose account is already an inactive mailbox, search by the address and it appears the same way.

You should seethe user listed with mailbox and archive ticked. If the archive box is missing, the user never had an archive mailbox enabled, so there is nothing extra to export.

3Step 3Run a search that covers the whole Office 365 mailbox

Open Searches, create a search, pick the data source you added and leave keywords and dates empty so every item matches. Click Run query, then Statistics to see item counts and the mailbox size for the mailbox and the archive. Note those numbers. They are your check at the end.

4Step 4Create the export with Create PSTs for messages

Click Export. Choose Export items with items report, then under Export format pick Create PSTs for messages. Set the Maximum PST package size: 10 GB gives fewer files, 5 GB is the default and both stay under the 20 GB the Import service wants if you ever bring the PST back into Office 365. Tick Organize data from different locations into separate folders or PSTs so the mailbox and archive land in their own PST files, and Include folder and path of the source so the Outlook folder tree survives.

You should seeCreate PSTs for messages selected, not Create .msg files. The MSG option gives you tens of thousands of loose files that Outlook cannot open as a mailbox and Mimecast will not take at all.

5Step 5Download the PST packages from Process manager

Open Process manager in the eDiscovery menu, select your export and wait for the status to read Completed. The Export packages section lists the ZIP files. Click Download packages. Packages expire 14 days after the export was created, so download them the same week. Office 365 does not keep a copy for you after that. Extract every ZIP into one folder: the PST files sit alongside Items.csv and Summary.html.

You should seeone or more PST files per data source, numbered when the mailbox exceeded the package size, plus the two report files. Keep the reports with the PST for the record.

6Step 6Open the PST in Outlook and compare the counts

On a PC with classic Outlook use File, Open & Export, Open Outlook Data File for each PST in turn. The folder tree from the mailbox appears. Compare the Inbox and Sent Items counts with the statistics from Step 3 and open one message with an attachment. If the PST is going to another system rather than staying in Outlook, the rules are in how to import PST to Office 365 and the email archive migration guide.

Export One Office 365 Mailbox to PST with Outlook

A user who wants a copy of their own Office 365 mailbox does not need Purview. Classic Outlook has the wizard under File, then Open & Export, then Import/Export. Choose Export to a file and pick Outlook Data File (.pst). Select the account at the top of the tree, tick Include subfolders, pick a location and choose how to handle duplicates. Finish, and Outlook writes the PST from the local cache. Two limits matter. Outlook exports what is in the offline cache, so in Cached Exchange Mode set the Mail to keep offline slider to All before you start or older mail is skipped. And the online archive mailbox is a separate root, so export it as a second PST.

Back Up Every Office 365 Mailbox to PST on a Schedule

Purview is a one-off export tool and Outlook is a one-user tool. Neither is a backup. If the goal is an Office 365 backup as PST files of every mailbox, refreshed weekly and stored outside Microsoft, the job wants a third-party backup tool that signs in to each account and downloads on a schedule.

1. Add the Microsoft 365 accountsOpen Univik Email Backup, choose Microsoft 365 and sign in to each mailbox. For a tenant, add a list of accounts instead. Modern authentication and app passwords are both supported.
2. Choose PST and the foldersPick PST as the output, keep the folder structure and select all folders or only the ones the policy needs. Set a split size if the PST should stay under a limit.
3. Set the scheduleDaily or weekly. After the first full run, later runs download only new mail, so a weekly backup of a busy tenant takes minutes rather than hours.
4. Store and verifyEach account gets its own PST on your disk or NAS. Open one in Outlook once a month to prove the backups restore.

Because the tool reads through IMAP and Graph rather than Purview, it needs no eDiscovery role and does not depend on the export packages or their 14-day expiry. It also covers Gmail, Yahoo and any IMAP account in the same run, which matters for companies with more than one mail platform.

Office 365 Export Mailbox to PST: Method Comparison

After the Office 365 PST Export

Store the PST with its Items.csv and Summary.html if it came from Purview, because those reports are what make the export defensible later. Keep each file under 20 GB if it may ever go back into Office 365 through the Import service. And if the export was for a leaver, decide now whether the licence can be released: converting the account to a shared mailbox, or making it an inactive mailbox under a retention or litigation hold, keeps the data in Microsoft 365 as well, which is often the safer pair with an offline PST.

Fix Common Office 365 PST Export Problems

Office 365 PST exports break in three predictable places. The red box is the symptom, the text under it is the repair.

Need PST copies of many mailboxes and not sure whether Purview or a backup tool fits? Tell our support team the mailbox count and how often you need the copies. We will recommend the route and the split size.

Office 365 PST export questions

Leena Taylor Paul

Written and maintained by Leena Taylor Paul and the Univik team, developers of Windows data conversion and recovery software since 2013. The Purview eDiscovery export steps and the 2025 retirement dates in this guide were checked against Microsoft's current documentation, and the screens are recreated from the Purview portal and classic Outlook so the labels match what you will see. Last verified September 2026. Need a hand? Contact our support team.

Sources checked: Microsoft Learn, Export search results in Purview eDiscovery · Microsoft Learn, Export Content Search results (retired, redirect notice) · Microsoft Support, Export emails, contacts and calendar items to a .pst file · Microsoft Learn, Overview of importing PST files to Microsoft 365

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