You can easily download files from Dotpost using the web app. (dotpost.com)

• Open your inbox 
• Click on the file you wish to download. 
• The file will now open in the PDF reader of your internet browser.
• From here you can download the file using the action in the menu. 
  • Different browsers use different terminology
    • Google Chrome - download
    • Microsoft Edge - save
    • Mozilla Firefox - download
    • Safari - share and then choose appropriate action e.g. Save to Files