Microsoft 365: what to count,
what it is worth.

At a glance

Unit to report	GB, split three ways: mailboxes, SharePoint, OneDrive. Mailbox item counts and user numbers go alongside if you have them.
Where the count lives	Microsoft 365 admin centre, Reports, then Usage. Exchange, then Mailbox usage, gives storage and item count per mailbox. SharePoint, then Site usage, gives files and storage per site. OneDrive usage does the same per user. Each report has an Export button.
Typical years retained	Mail and files stay until someone deletes them or a retention policy removes them. The Create date column in Mailbox usage shows when each mailbox began; the oldest is your start year. Check your retention policies in Purview before assuming the whole history is there.
What usually makes it valuable	Email threads where decisions were argued through, Teams channel conversations, meeting recordings and transcripts, and document version histories showing how work was drafted and revised.
What stays private	Every name, address and identifier of staff, customers and counterparties. Client material held under their agreements. Licensed third-party content. Guest and external users' contributions.

Paths checked against Microsoft Learn: Exchange Mailbox usage report, SharePoint site usage report and Export search results in eDiscovery. The admin centre moves reports between tabs, so check in your version.

Where the count lives

Nothing needs exporting. Three usage reports, all read from the admin centre.

1. Sign in to the Microsoft 365 admin centre with a role that can view usage reports: Global Administrator, Exchange Administrator, SharePoint Administrator, Reports Reader or Usage Summary Reports Reader.
2. In the left navigation choose Reports (under Show all if it is hidden), then Usage.
3. Mail. Under Reports choose Exchange, then View More under Email activity, and switch the drop-down to Mailbox usage. The table lists every mailbox with Item count, Storage used (MB) and Create date. Click Export to get a CSV and sum the columns, or read the Storage chart total. Switch the selector to Shared to add shared mailboxes.
4. Files. Back on Usage choose SharePoint, then the Site usage tab. Each site shows Files and Storage used (MB); the chart gives the organisation total. OneDrive usage works the same way per user.
5. Teams. The Teams reports on the same Usage page cover recent activity only. For the intake, say how long Teams has been in use and whether channel chat or meetings dominate; the message count is not needed.
6. Years: sort Mailbox usage by Create date. The oldest mailbox, usually the founder's, gives the start year. Usernames are concealed by default in these reports; you do not need to reveal them for the count.

The activity trends in these reports cover the last 7 to 180 days. Storage and item counts are current totals, which is what the intake asks for.

What to put in the intake

Field	What to enter	Example
Volume	Mailbox GB, SharePoint GB and OneDrive GB, with the user count.	Mail 310 GB, SharePoint 1.2 TB, OneDrive 640 GB, 45 users
Years covered	Start year from the oldest mailbox, any migration in (from Exchange on-premises or Google Workspace), and whether a retention policy trims old mail.	2014 to now, migrated from on-premises Exchange in 2016
Estimate	Tick it if you read the chart rather than summing the export.	Ticked

Estimates are fine. The Storage chart total on each report is close enough.

Why buyers value it

A business's Microsoft 365 tenant is its working record in full sentences. Email threads hold the back and forth that produced decisions: the question, the pushback, the compromise, the sign-off, each with a timestamp and a role. Teams channels hold the same thing at a faster tempo, with the meeting that resolved it recorded and transcribed alongside. SharePoint and OneDrive keep every version of every document, so a buyer sees how a proposal, a policy or a contract was drafted and revised rather than only the final copy. Calendar patterns show how the organisation actually spent its time. Buyers pay for the thread that argued the decision through, not the deck that announced it, and this is where those threads live.

What stays private

• Names, email addresses, phone numbers, addresses, account numbers and the rest of the 60+ identifier types are irreversibly removed from every message, transcript and document before any buyer sees anything, with each removal written to the audit ledger. People become stable role labels.
• Material you hold for clients under their agreements, and licensed third-party content such as purchased reports, stock imagery or supplier catalogues, is filtered out at extraction.
• Contributions from guest and external users are excluded. Payroll, HR files and anything in a sensitive category are excluded at extraction.
• Buyers receive a prepared, de-identified copy under licence, never access to the tenant and never the raw export. The Trust and Security pages cover the full process.

If you want to export the full history

1. Sign in to the Microsoft Purview portal with an account that has eDiscovery permissions and a Microsoft 365 E3 or E5 licence. Exporting SharePoint content also needs a SharePoint E3 licence on that account.
2. Open the eDiscovery solution card, then Cases. Create a case, open the Searches tab and create a search covering all mailboxes, SharePoint sites and OneDrive accounts, with the date range you need. Run Generate statistics first on a large tenant; it speeds the export.
3. Open the search and choose Export. Give it a name, choose Export items with items report, then either Create PSTs for messages or Create .msg files for messages. Tick Include Teams and Viva Engage conversations and set document versions to All versions if you want the revision history. Select Export.
4. Track progress under Process manager and download the packages from there. Search export packages expire 14 days after creation, so download promptly and split very large exports by date range.

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