If you want to convert MBOX to O365 Effortlessly & directly, then I suggest The WholeClear MBOX to Office 365 Converter is a reliable solution that makes it easy to move MBOX files to Office 365 (Exchange Online) without any problems. In my experience, it sends emails, folders, and attachments right to your Microsoft 365 mailbox without needing any other programs. The UI is easy to use, and it works well with big MBOX files.

Important Features

Directly moving MBOX to Office 365.
Keeps the folder structure, metadata, and attachments.
Can import many MBOX files at once.
Authentication for Office 365 that is safe.
Simple and easy-to-use UI.
No need for Outlook or other apps.