If you want to easily import MBOX files into an Office 365 account, try trying the BLR Tools MBOX Converter  Tool. Users can quickly move MBOX emails to other email clients & file formats, like MSG, PDF, TXT, & PST. Also, users can import MBOX emails into a variety of email clients, including Outlook, Gmail, Yahoo, Opera Mail, and others. To fulfill their regular requests, users can quickly import one or more MBOX files into the email apps of their choice. All MBOX emails and attachments can be exported to other email applications by email users. Users can quickly search the MBOX file from local system using its auto-search features. Users can quickly move files of any size with MBOX. By filtering & choosing the required emails using the date range feature settings, users can migrate emails within a certain time window. Users can convert up to 15 email items for free in the trial version that is offered for evaluation.