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Bindu M S 60 Reputation points
2026-06-16T04:54:30.5266667+00:00

We are currently using Microsoft 365 Business Basic licenses in our organization. Several users have been experiencing mailbox storage issues due to large volumes of email data. For some users, we have already extended the mailbox storage by an additional 100 GB. However, we are now facing a similar issue with another mailbox where the archive storage is also nearing its capacity limit

 

I want to know whether it is possible to take a backup of the mailbox and archive data in PST format.

 

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Anonymous
2026-06-16T05:54:13.6666667+00:00

Hi @Bindu M S

Mailbox and archive mailbox data can be exported to PST format using Microsoft Purview eDiscovery (Content Search) tools, subject to the permissions and export features available in your tenant.

However, exporting to PST is generally intended for compliance, legal, or data extraction scenarios rather than ongoing mailbox management.

Before proceeding with a PST export, it’s recommended to review the user’s licensing. Microsoft 365 Business Basic includes a 50 GB primary mailbox, while larger mailbox quotas, Online Archive, and advanced features such as auto-expanding archiving require additional licensing (for example, Exchange Online Archiving add-on or Exchange Online Plan 2)

Before considering PST exports, you may want to verify:

  • Whether the affected user has an Online Archive mailbox enabled
  • Whether auto-expanding archiving is enabled for the archive mailbox
  • The current size of both the primary mailbox and the archive mailbox

You can check the archive status using Exchange Online PowerShell:

Get-Mailbox ******@domain.com | FL ArchiveStatus,AutoExpandingArchiveEnabled

If the archive mailbox is already nearing its limit and auto-expanding archiving is not enabled or not available with the current license, exporting older data to PST and subsequently removing those items from the mailbox can be used as a temporary workaround to reduce mailbox usage, but it does not provide ongoing storage management.

While PST export is possible (and useful for one-time extraction or compliance scenarios), it is not intended as a scalable or long-term solution.

Enabling archive features, especially auto-expanding archiving, which can increase archive capacity up to approximately 1.5 TB depending on licensing, is typically a more effective approach for managing large mailbox growth.

I hope this information is helpful.

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  1. AI answer

    2026-06-16T04:54:46.8166667+00:00

    Yes, it is possible to back up mailbox and archive data to PST, but it is not the recommended approach for Exchange Online.

    Key points for Microsoft 365 Business Basic (Exchange Online Plan 1):

    1. Recommended approach: use Exchange Online Archiving
    • Exchange Online does not support traditional mailbox backups and restores (no point-in-time restore of a mailbox).
    • For additional storage, the recommended solution is Exchange Online Archiving, including auto-expanding archiving, which can provide up to 1.5 TB of archive storage (per the applicable licensing and configuration).
    • Using PSTs for long-term storage reduces discoverability and control of content and is therefore not recommended for production/compliance scenarios.
    1. PST backup is technically possible from Outlook If still required (for example, for local/offline copy or offboarding scenarios), users can export mailbox data to PST using Outlook:
    • In Outlook: File → Open & Export → Import/Export → Export to a file → Outlook Data File (.pst).
    • Select the mailbox folders (including archive folders if they are visible in Outlook) and export.
    • The resulting PST can be stored locally and later re-opened or imported.
    1. Limitations and considerations
    • PST-based backups are not centrally managed by Exchange Online and are outside Microsoft 365 compliance, retention, and eDiscovery controls.
    • PST files can be lost or corrupted and are not a substitute for compliance-grade archiving.
    • If the goal is to handle capacity issues, enabling/optimizing archive mailboxes and auto-expanding archiving is the supported method rather than offloading to PST.
    1. Offboarding / license removal scenarios
    • After a license is removed, mailbox data is retained for 30 days by default, during which time it can be exported to PST if needed.

    In summary: exporting to PST from Outlook is possible for both primary and archive mailboxes, but for ongoing capacity and compliance needs in Exchange Online, Exchange Online Archiving and auto-expanding archiving should be used instead of PST backups.

    References:

    AI-generated content may be incorrect. Read our transparency notes for more information.

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