If user is moving Thunderbird to Outlook they need to convert the MBOX to PST, so MBOX file data will become accessible in Outlook. To convert MBOX to PST, we can use Shoviv's MBOX to PST Converter Tool to become more efficient and productive. A free trial facility is available to test out software, and Shoviv Software lets you install the tool without asking for any details. https://www.shoviv.com/blog/export-emails-from-thunderbird-to-outlook-2016-2019/