To avoid data loss during PST to MBOX migration, don’t directly experiment with the original PST file. Always make a duplicate copy first. Also, check whether the conversion method supports attachments, folder structure, email formatting, and metadata because these are the areas where data usually gets disturbed.

I personally tested Softaken PST to MBOX Converter for this type of Outlook PST to MBOX conversion. It was useful because it showed the PST mailbox structure before export and allowed selective conversion. That helped avoid unnecessary mailbox data export and reduced the chance of confusion after migration.

The converted MBOX file can be used with clients like Thunderbird, Apple Mail, Eudora, and Entourage. For large PST files, convert folder-wise if possible and verify the output after conversion.

Here is the tool page: https://www.softaken.com/pst-to-mbox-converter