The best way to clean duplicate MSG files without Outlook then I can suggest a reliable duplicate-removal tool like TrustVare MSG Duplicate Remover, which works independently of Outlook. It can scan folders of MSG files to detect duplicates based on subject, sender, date, and content, and remove them without losing important data or information. It doesn't require Outlook to be installed on the PC. It can handle multiple duplicate MSG files without facing any issues. The tool can provieds a free trial to test the tool before buying it. You can see the preview of duplicate deletion and decide which one move or delete.