No matter what kind of file it is, an application/octet-stream attachment is rarely viewable in an email or web client. If you are using a workstation-based client, such as Thunderbird or Outlook, the application should be able to extract and download the attachment automatically. After downloading an attachment through any of these methods, you must then open the attachment in the appropriate application to view its contents. Before opening attachments, even from trusted senders, you should follow the guidelines listed in. In addition to the generic application/octet-stream content type, you may also encounter attachments that have different subtypes (e.g., application/postscript, application/x-macbinary, and application-msword). They are similar to application/octet-stream, but apply to specific kinds of files.