Email Migration Guide

Google Vault to Office 365 MigrationExport the matters, rebuild the folders, import the PST files

Google Vault to Office 365 migration: export Gmail matters as PST or MBOX, fix the single-folder export, split under 20 GB and import into Microsoft 365.

By 📅 Updated: September 7, 2026 ⏲️ 12 min read ✓ Verified against Microsoft's published documentation 🖼️ 5 screens

A Google Vault to Office 365 migration has three parts. In Vault, create a matter, search Gmail for the accounts and date range you need and run a Google Vault export to PST or MBOX; the download is available for 15 days. A Vault export puts every message in one flat folder with no labels. Run the files through Univik Google Vault Converter to rebuild Gmail labels as Outlook folders and write one PST per user under 20 GB. Then import the PST files with the Office 365 Import service. Microsoft's own Google Workspace migration copies live mailboxes only, so anything that exists only in Vault has to take this route.

The Workspace contract is ending and the mailboxes are moving to Microsoft 365. The live mail is the easy half; Microsoft has a migration batch for that. The hard half is Google Vault. It holds years of retained mail, including messages users deleted long ago, kept for legal reasons and invisible to any mailbox migration. Get it out wrong and it lands in Outlook as one folder of 400,000 messages. Get it out late and the export has expired. This guide covers the Vault export as it works in 2026, the label problem, the conversion and the Microsoft 365 import, in the order that avoids both mistakes.

Before You Migrate Google Vault to Office 365

TimeDays
DifficultyMedium to hard
CostVault export free
Runs onBrowser + Windows

What are you actually trying to move? Pick the card and it takes you to the part that matters.

Everything Vault holds, before the Workspace contract ends Retained mail for every user, including deleted messages the mailbox migration will never see. Export by organisational unit, convert, import into Office 365 archive mailboxes. Start with the export → A Vault PST that opened in Outlook as one giant folder That is how Vault exports work. Labels are not folders. The fix is a conversion that reads the metadata XML and rebuilds them. See the folder fix → Not sure whether you need Vault at all If every message you care about is still in the live mailboxes, Microsoft's Google Workspace migration batch may be enough. The comparison shows where it stops. Compare the routes →
Have these in place first
  • A Vault licence on every account you exportVault only holds data for licensed users. Delete a user or remove the licence and the retained data can be purged at once. Keep licences until the Microsoft 365 import is verified.
  • Vault privileges: Manage Matters, Manage Searches, Manage ExportsA super admin does not have them by default. Assign the Vault privileges to the account doing the work.
  • Disk space for the download and the conversionVault ZIP files, the extracted PST or MBOX files and the converted output can each be the size of the archive. Budget three times the total.
  • Microsoft 365 licences with archive mailboxes enabledVault data belongs in the users' archive mailboxes. Enable Exchange Online Archiving before the import and read the 20 GB per PST rule in the Import PST to Office 365 guide.
Five words this guide leans on
Matter
A Vault container for one eDiscovery job: its searches, exports and holds. Everything you export lives under a matter. Vault calls each account in scope a custodian.
Hold
A Vault rule that keeps data regardless of retention rules and stops the account being deleted. Holds must be lifted, deliberately and after the migration, before accounts go.
Export
Vault's output of a search as PST or MBOX files inside ZIP archives, plus a metadata XML, a result counts CSV and an errors XML. It is available for 15 days.
Metadata XML
The file beside the mail that lists every exported message with its labels, account and Message-ID. It is the only place Gmail labels survive in a Vault export.
Import service
Microsoft Purview's route for bringing PST files into mailboxes or archive mailboxes, by network upload or drive shipping, with a retention hold applied.

Export Gmail from Google Vault in 5 Steps

Vault exports are search results. There is no export whole archive button, so the search has to be wide enough to catch everything and small enough to finish inside Vault's 24 hour processing window.

1

Create a matter for the Google Vault export

Sign in at vault.google.com and open Matters, then Create. Name it for the job, such as Workspace exit - Gmail archive 2016-2026. A matter is a container; you will run several searches and exports inside it, one per organisational unit or per year. Each stays listed here with its own download.

Google Vault · MattersScreen 1 of 5
Swipe sideways to see the whole screen

Step 1Matters. One matter for the migration, with a search and export per organisational unit inside it.

2

Search Gmail for the accounts and the date range

Inside the matter, open Search. Set the service to Gmail. For entity choose Organizational unit and pick one OU at a time, or Specific accounts for up to 500 custodian addresses. All accounts works for a small domain but produces one export too large to finish. Set the sent date range to cover the whole retention period and leave the terms box empty so every message matches. Click Count first. The number tells you whether to split the search by year before you export.

You should seea count per account. Anything over a few hundred thousand messages in one export is a candidate for splitting by year, because Vault stops processing at 24 hours and marks the export partial.

Google Vault · SearchScreen 2 of 5
Swipe sideways to see the whole screen

Step 2Gmail, one organisational unit, full date range, no terms. Count before you export.

3

Export the Google Vault search as PST or MBOX

Click Export, name it and choose the format. PST is the obvious choice for an Office 365 destination. A Google Vault export to PST splits into 1 GB files per account. MBOX processes faster and splits into 10 GB files. Either is fine when a converter sits in the middle, so pick MBOX for very large OUs to get the export done inside the window and PST for smaller ones. Both formats have the same limitation described in the next section: no folders.

Google Vault · Export optionsScreen 3 of 5
Swipe sideways to see the whole screen

Step 3PST or MBOX. PST splits at 1 GB per account and MBOX at 10 GB. Neither keeps labels as folders.

4

Download the Google Vault export within 15 days

Open the matter's Exports tab. Large exports take hours; Vault emails you when one completes. Download every ZIP part plus the three side files: the metadata XML, the result counts CSV and the errors XML. Exports are deleted 15 days after they were started and cannot be recovered, only re-run. Put the downloads on a drive with room to extract them, and extract the ZIP files there.

You should seeone or more ZIP files per export, each holding PST or MBOX files named account-randomstring, plus metadata, counts and errors files that share the export name. If a conversion_errors ZIP appears, it holds messages Vault could not write to PST as EML files.

Google Vault · ExportsScreen 4 of 5
Swipe sideways to see the whole screen

Step 4Download every ZIP and the three side files before the 15 days run out.

5

Check the counts and open one Vault PST to see the single-folder problem

Open the result counts CSV and add up the messages per account. Then attach one of the PST files in classic Outlook through File, Open & Export, Open Outlook Data File. It opens as a single folder named after the account with every message in it: Inbox, Sent, Spam and Trash mixed together, with the account split across several 1 GB files. That is a correct Vault export. It is also not what a user or an import should receive, which is why the next two sections exist.

Windows Explorer · Extracted exportScreen 5 of 5
Swipe sideways to see the whole screen

Step 5One account, three PST parts of 1 GB each, plus the metadata XML that holds the labels.

The Single-Folder Problem in Every Google Vault Export

Gmail has no folders. It has labels, and a message can carry several. When Vault writes a PST or MBOX it drops the labels from the message and records them in the metadata XML instead. Google's own documentation says it plainly: the labels used in Gmail to classify messages are not converted into mailbox folders, and all messages appear in a single folder. Vault does not add the X-Gmail-Labels header that Google Takeout adds either.

For an eDiscovery review that is fine. For an Office 365 migration it is a problem three times over. Users get one folder of everything they ever sent, received or binned. The Microsoft 365 Import service writes that flat pile into the archive mailbox exactly as it is. And each account arrives as a stack of 1 GB PST parts that each need their own row in the mapping file. The fix is to rebuild the structure from the XML before anything is imported.

What the metadata XML holds

One record per message with the account it belongs to, its Message-ID, Gmail's internal date and every label on it. A converter that reads the XML alongside the mail can put a message with the labels Inbox and Vendors into an Inbox folder and a Vendors folder. Spam and Trash go into their own folders, where they can be excluded.

Convert Google Vault Exports to Import-Ready PST

This is the step in a Google Vault to Office 365 migration that Google does not offer and Microsoft does not need to know about. Univik Google Vault Converter reads the Vault ZIP files directly, links each message to its record in the metadata XML and writes output the Office 365 Import service is happy with.

  1. Add the Vault ZIP filesClick Add ZIP and select every part of the export. The converter reads the PST or MBOX content and the metadata XML together, so there is nothing to extract or match by hand.
  2. Filter to the scope you needPreview by account, date range and label. Exclude Spam and Trash if policy allows, or keep them in their own folders for the legal team.
  3. Rebuild folders and choose PST per userLabels become Outlook folders: Inbox, Sent, Drafts and every custom label. Output is one Unicode PST per account, so the three or four 1 GB Vault parts for a user merge into one file, or into numbered parts under 20 GB for the largest mailboxes.
  4. Read the reportThe post-conversion report lists messages per account and flags anything from the Vault errors file, which is the evidence you keep with the export.

The conversion runs offline on a Windows PC and needs neither Outlook nor a Google API connection. Vault exports that contain Chat and Groups data alongside Gmail are separated by service in the output, so the Gmail PST files go to the Import service and the Chat transcripts go wherever your records policy sends them.

Turn Vault ZIP exports into per-user PST files with Gmail labels as folders

Univik Google Vault Converter reads Vault PST and MBOX exports with the metadata XML. It rebuilds labels as Outlook folders, writes one Unicode PST per account and reports every message against the Vault error file. Nothing goes back to Google.

⬇️ Download Free Trial See All Features →

Windows 11 / 10 · works on the downloaded export offline · trial output for a sample of every account, so you open a PST before paying

Import the Google Vault PST Files into Office 365

From here the job is the standard one described in how to import PST to Office 365: create an import job in Purview, upload with AzCopy, fill the mapping file, run the job. The Google Vault specifics are these.

Run the import while the Workspace licences are still active. Only when the Office 365 side has been verified should Vault holds be released and accounts deleted, because that deletion is what purges the Google copy.

Google Vault Export vs the Other Two Routes to Microsoft 365

RouteWhat it movesDeleted but retained mailFoldersEffortUse it for
Microsoft Google Workspace migration batch (Exchange admin center)Mail, calendar, contacts in the live mailboxNoLabels become foldersLowEvery active user's current mailbox
Google Vault export + converter + Import serviceEverything Vault retains for the accounts you chooseYesRebuilt from XMLMediumRetention data, leavers, legal holds
Workspace Data Export tool (Admin console)Whole organisation to a Cloud Storage bucket, once per 30 daysVault data included, flatDepends on formatHighA full-tenant copy for the record, not a per-user migration

Most Google Vault to Office 365 projects use the first two together. The migration batch moves the live mailboxes into Office 365 on the cutover weekend. The Vault export moves the retained history into archive mailboxes in the weeks around it.

After the Google Vault to Office 365 Migration

The Vault migration is complete when
  • The result counts CSV totals match the converted PST counts, and the import jobs for every account show Completed in Purview
  • A user opens their Microsoft 365 archive mailbox and finds Gmail labels as folders under the root you set, with a 2016 message and its attachment intact
  • Legal has the metadata XML, the errors XML and the conversion reports filed with the PST copies. Legal has also agreed which Vault holds can be released

Only then release the holds in Vault, let retention rules expire the data or delete the accounts. Keep the downloaded Vault ZIP files on backed-up storage for as long as your policy requires, because they cannot be re-downloaded and re-exporting needs a live Workspace subscription. The email archive migration guide covers the same journey for archives that are not Google, and how to split a large PST file helps when a single account comes out over 20 GB.

Fix Common Google Vault Migration Problems

Vault migrations trip on three things. Each red You see box is paired with its green Do this repair.

1The export says Export contains partial results

Do this: Vault stopped after 24 hours. Continue the export for another 24, then re-run the search split by year or by smaller organisational unit. MBOX exports process faster than PST if the window is still too tight.

2The PST opens in Outlook as one folder with everything in it

Do this: That is normal for a Vault export; labels are only in the metadata XML. Convert the export with the XML alongside so labels become folders, then import the converted PST, not the Vault one.

3The Import job fails for some users with mailbox not found

Do this: The Gmail address has no matching Microsoft 365 mailbox, usually a leaver. Create an inactive or shared mailbox for them, or map their Vault data to a manager's archive under a named TargetRootFolder, and retry those rows.

Have a Vault export downloading and a Workspace end date in view? Tell our support team the account count and the total size. We will confirm the conversion plan and the PST sizes before the clock runs out.

Google Vault migration questions

Can Google Vault export directly to Office 365?
No. Vault exports to PST or MBOX files that you download. Getting them into Microsoft 365 is a separate step through the Import service, and a conversion in between is what turns the flat single-folder export into per-user PST files with folders.
Does a Google Vault PST export keep Gmail labels as folders?
No. Google states that labels are not converted into mailbox folders and all messages appear in a single folder in PST and MBOX exports. The labels are recorded in the metadata XML, which is why a converter that reads the XML can rebuild them.
How long is a Google Vault export available?
15 days from the moment you start the export. After that the files are deleted and the only option is to run the search and export again, which needs the accounts to still be licensed for Vault.
Do I need a special Google Workspace edition for Vault?
Vault is included in Business Plus, Enterprise Standard and Plus, Frontline Standard and Plus, the Education editions and Enterprise Essentials Plus. Other editions can buy it as an add-on licence. Every account you export must hold a Vault licence.
Will deleting a Google Workspace user lose their Vault data?
Yes. Google warns that deleting a user or removing their licence can purge the retained data at once, with no recovery. Keep licences and holds in place until the Microsoft 365 import has been checked, then remove them.
Should I export from Vault as MBOX or PST for Office 365?
Either works when a converter rebuilds the folders. PST is split into 1 GB files per account and is slower to produce; MBOX is split at 10 GB and processes faster. For very large organisational units choose MBOX so the export finishes inside Vault's 24 hour window.
About This Guide

Written and maintained by and the Univik team, developers of Windows data conversion and recovery software since 2013. The Vault export behaviour, file splits, 15 day expiry and licensing in this guide were checked against Google Workspace Admin Help, and the Microsoft 365 Import limits against Microsoft Learn. Last verified September 7, 2026. Need a hand? Contact our support team.

Sources checked: Google Vault Help, Export data from Vault · Google Vault Help, Contents of a Vault export · Google Vault Help, Review messages exported with Vault · Google Vault Help, Supported editions and services · Microsoft Learn, Perform a Google Workspace migration · Microsoft Learn, Overview of importing PST files to Microsoft 365

Email MigrationHow to Import PST to Office 365 by Network Upload or Drive Shipping11 min read OutlookHow to Split a Large PST File: Outlook's Built-in Ways and the PST Splitter Route10 min read Email MigrationEmail Archive Migration: How to Plan and Run It Without Losing a Message12 min read