Download and run this windows-based Apple Mail email converter tool. Hit on Add File/Folder button and chose Select file or Select folder option. Input Apple Mail MBOX files and hit on Next to load them into the software. Read emails & select mail folders that required and click on Convert MBOX. Choose the file type in which you want to Convert Apple Mail emails. (PST, EML, EMLX, HTML, MHT, NSF, Thunderbird, Zimbra, etc.) Apply required settings Mail filter, naming convention, and saving location. Lastly, click on Convert and begin the Apple Mail email conversion process.