Back up to pst

Hi Stephanie Bunker

Mailbox and archive mailbox data can be exported to PST format using Microsoft Purview eDiscovery (Content Search), provided the necessary permissions and export capabilities are available in your Microsoft 365 tenant.

However, PST exports are primarily designed for compliance, legal, investigation, or one-time data extraction purposes rather than ongoing mailbox storage management.

Before proceeding with a PST export, it is recommended to review the user's current licensing. Microsoft 365 Business Basic includes a 50 GB primary mailbox. Additional mailbox capacity, Online Archive, and advanced archiving features such as auto-expanding archiving require additional licensing, such as the Exchange Online Archiving add-on or Exchange Online Plan 2.

Prior to considering a PST export, you may want to verify the following:

• Whether an Online Archive mailbox is enabled for the affected user.
• 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 configuration using Exchange Online PowerShell:

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

If the archive mailbox is approaching its storage limit and auto-expanding archiving is either unavailable or not enabled under the current licensing, exporting older mailbox data to a PST file and then removing those items from the mailbox can serve as a temporary measure to reduce mailbox usage. However, this approach does not provide a sustainable long-term storage solution.

While PST export remains a viable option for one-time data extraction and compliance-related requirements, it is not intended to be a scalable mailbox management strategy. Enabling Online Archive features, particularly auto-expanding archiving, is generally the preferred approach for organizations managing significant mailbox growth. Depending on licensing eligibility, auto-expanding archiving can increase archive storage capacity to approximately 1.5 TB, providing a more effective long-term solution for mailbox retention and storage management.

I hope this information and if you have any futher questions, please feel free to ask via comment section.

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Both types of data can be backed to PSTs, yes. But you shouldn't. PSTs are prone to corruption and a nightmare from security perspective, they should be avoided. Moreover, by exporting the data outside of Microsoft 365, you loose the integration with search, compliance features, or even Copilot (if you are using it).

In most scenarios, keeping the data within the Microsoft 365 boundary is recommended. In your scenarios, assigning an Exchange Online Plan 2 (or equivalent) license to the mailbox should be the easiest solution, as it enables the so-called "auto-expanding" archive functionality and allows the mailbox to grow to 1.5Tb. Here's the relevant documentation: https://learn.microsoft.com/en-us/purview/enable-autoexpanding-archiving

Auto-expanding archives are integrated with the Microsoft compliance stack, so if you need to meet regulatory requirements, you get this out of the box with support for retention and holds.