The most efficient way to transfer Mac Mail emails to Microsoft Outlook is by converting the Apple Mail MBOX files to Outlook importable PST format by using an MBOX to PST converter tool, such as Stellar Converter for MBOX. If you want to transfer Mac emails to Outlook, there is no direct way to do so. However, Outlook stores the data in OLM file on Mac and OST/PST File on Windows system, based on the type of email account configured.

The Mac Mail app stores the mailbox items, such as emails, attachments, contacts, etc., in MBOX file format. Outlook, on the other hand, is available for both Mac and Windows PC. Apple Mail, also referred to as Mac Mail, is the default email client in macOS machines.