If you want to preview files in Windows 11/10 without opening them, then you can use QuickLook, File Viewer Plus, One Commander, or Seer app.

Windows Vista only: Vista's Preview Pane can be helpful in determining exactly which file you're looking to open, and PreviewConfig lets you extend its usefulness beyond the handful of files Vista ...

Given how limited the preview pane already feels in Windows 10, even adding just two more file types feels like a huge improvement.

Download Preview Handler Association Editor to enable Windows Explorer preview pane in Windows 11/10. The tool lets you preview EML and other file types files in Windows File Explorer.