Can the Outlook mails be directly transferred to MBOX format?

Answer 1

Not directly. Apple Mail and Outlook manage their mails in separate formats. Thunderbird files are well supportive in the Mac client. Outlook in Mac can export in OLM format, and Apple Mail can only import in MBOX format.

To import the archived Outlook files to Apple Mail, you need to convert OLM files to Apple Mail archive. This conversion can not be done directly. There is no free solution to this as well. You would need to get a paid tool. There are paid tools to convert an Outlook PST file to MBOX format to transfer Outlook mails to MBOX.