A MIME attachment with the content type "application/octet-stream" is a binary file. Typically, it will be an application or a document that must be opened in an application, such as a spreadsheet or word processor. If the attachment has a filename extension associated with it, you may be able to tell what kind of file it is. A .exe extension, for example, indicates it is a Windows or DOS program (executable), while a file ending in .doc is probably meant to be opened in Microsoft Word.
No matter what kind of file it is, an application/octet-stream attachment is rarely viewable in an email, Usenet, or web client. If you are using a text-based client, such as Pine, trn, or Lynx, save the attachment to your account, and then transfer it to your personal computer using SFTP. IU Webmail allows you to save attachments directly to your personal computer; see In IU Webmail, how do I use attachments? 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.
Note: Before opening attachments, even from trusted senders, you should follow the guidelines listed in Best practices for computer security.
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.
Alternative information to this article via sillydog.
I had the exact same problem and I just cracked it.
You have to go to Edit\Preferences\Advanced\HTTP Networking and select "HTTP 1.0" instead of "HTTP 1.1". I am sure this will help!