Preserving folder organization depends on how the source MBOX archive is structured and how the destination email application handles imported messages. Some manual methods import messages into a single mailbox, requiring you to create folders and reorganize everything afterward.
Before transferring your archive, inspect the available folders and determine how they should appear in the destination IMAP account. Choose a migration method that supports folder selection or folder mapping instead of relying entirely on drag-and-drop.
MacSonik MBOX Converter is one option to consider because it supports transferring MBOX data to IMAP servers. Review the folder-selection options and verify the results after migration rather than assuming the hierarchy will be preserved automatically https://www.macsonik.com/mbox/converter/