To convert bulk Thunderbird MBOX files in Outlook, use eSoftTools Thunderbird to Outlook Converter Tool. It can convert bulk MBOX folders in Outlook without any changes to their bcc, cc, from, dates, attachments, and email headers, among other things. It can alter any size of Thunderbird MBOX folder data, and there are no data size limits for conversion. It may let users get a free trial pack that allows them to export the first 25 items from Thunderbird.
For more info:- Convert bulk Thunderbird MBOX files in Outlook