I’m working with a Microsoft 365 mailbox that has accumulated years of archived emails, and I need to create PST files for local storage. The archive is quite large, so I’m trying to find a reliable way to handle the export without making the process unnecessarily complicated.

My first option was Outlook because the Online Archive is already visible there. The built-in Import/Export feature allows an archive mailbox or selected folders to be saved as a PST, including subfolders. That seems reasonable for smaller archives, but I’m not sure how practical it is when the mailbox contains a very large amount of historical data.

The biggest concern is the time involved. A large export can take a long time, and if Outlook stops responding, the system restarts, or the export encounters an error, it may be difficult to know exactly what has already been processed. I also need enough local storage for the resulting PST files.

While researching Export Online Archive to PST  methods, I found that date-based filtering can make large exports easier to organize. Instead of selecting everything at once, the archive can be divided into manageable periods and checked individually. This would also make it easier to verify important folders, attachments, and older messages after each export.

I also came across the SysInfo Office 365 to PST Export Tool. Its information mentions support for Archive, Primary, Shared, and Public mailboxes without requiring Outlook. It also includes date filtering, duplicate removal, skipping previously migrated items, and options for splitting large PST files.

For an Office 365 archive mailbox to pst backup, I’m mainly interested in reducing the risk of having to restart the entire operation. Has anyone handled a large Online Archive this way? Would you recommend exporting by date range and verifying each PST separately?