Email and calendar
Find and export
your Outlook data.
For company Outlook accounts hosted in Microsoft 365, Exchange reports primary-mailbox storage. Archive and retained former-employee mailboxes need an additional check to describe the full history.
- Report in
- GB
- Category
- Email and calendar
- Last checked
Find your Outlook data size
- Use the Microsoft 365 admin center with a role allowed to read usage reports.
- Open Reports → Usage and find Exchange → Mailbox usage.
- Export the mailbox table to CSV and sum Storage used (MB), converting to GB by dividing by 1,024.
- Ask your Exchange administrator for archive-mailbox sizes and retained inactive-mailbox storage. Identify those additions separately.
- For a single mailbox, use Exchange admin center → Recipients → Mailboxes and inspect its usage.
What to include in your data inventory
Report primary and archive email storage in GB, with the number of user, shared and retained inactive mailboxes. Describe any recoverable or held content counted separately.
Use the oldest retained email date for the years covered, particularly if mail was imported from another service. Mailbox creation dates alone can miss that history.
Export your Outlook history
- Have your Microsoft 365 administrator confirm eDiscovery permissions and licensing.
- In Microsoft Purview → eDiscovery → Cases, create a search for the mailboxes and date range agreed for the dataset.
- Choose Export, include the required mailbox items and select Create PSTs for messages. Review the departed-user option when collecting retained former-employee mail.
- Download the packages from Process manager before they expire, keeping the item reports alongside the PST files.
- For one account in classic Outlook for Windows, use File → Open & Export → Import/Export → Export to a file → Outlook Data File (.pst) and include subfolders.
Purview search exports expire after 14 days. Primary and associated archive content can be combined in a mailbox's exported PST.
A local Outlook export only includes the content available to that client. Confirm synchronization and export scope before treating it as the whole mailbox.
Why Outlook data has value for AI training
Business email links customer and supplier requests to the replies, approvals and documents that followed. Message threads help preserve that sequence.
Calendar and attachment context can add useful detail about how work was organized across teams.
What stays private
Select the mailboxes and dates to include. Retained legal, executive or personnel archives can remain outside the proposed dataset.
Telegraph Lab reviews the proposed material with you and agrees how sensitive information will be handled. Preparation can include excluding material, redacting details and replacing personal identifiers. Your company keeps ownership; the licensing agreement defines the material, permitted uses and authorized recipients.
Common questions about Outlook data
Does Mailbox usage include archive storage?
Microsoft's storage chart excludes archive mailboxes. Ask the Exchange administrator for those sizes separately.
Can a shared mailbox count toward the volume?
Yes, when it is retained and in scope. Include its storage and identify it as a shared mailbox.
Can we recover every former employee's mail?
Availability depends on whether the mailbox was retained or placed under a suitable hold before deletion. Ask your administrator what still exists.
Can a user export their own mailbox?
Classic Outlook for Windows supports PST export. For company-wide collection, an administrator can use Purview with the required permissions and licenses.