The common exchange formats for email are MIME (.eml) and Mbox (.mbox) which are both supported for import.
One multiple files with either MIME or Mbox data can be uploaded to add email messages to the currently selected folder:
Messages from your inbox or any other folder can be downloaded to your computer for archiving or backup. When exporting, messages will be saved as single .eml files.
To download an email message, select one first a message first in the Messages List and then choose Download (.eml) from the More menu in the toolbar. Choose where to save the exported .eml file if prompted, otherwise find the file the “Downloads” folder on your computer.