One or multiple files with either MIME or Mbox data can be uploaded to add email messages to the currently selected folder:
• Click the folder where the imported messages should be added.
• Select Import messages from the Folder actions menu behind the gear icon in the folders list footer.
• Select the file to import from your computer’s hard drive. You can select multiple files in the file picker dialog by holding down the Shift or Ctrl keys while selecting a file.
• Press Upload to start the import process.