Just a quick follow-up to my post. The header that's being recognized as an application/octet-stream is a Zip PK header. It's slightly different (as I showed) because. To open an unidentified file, you need to either figure out which program can open the file as a document or change the file's extension to run as a program. When attached to an email, save the octet-stream before opening it. Software to open or convert OCTET STREAM files It looks like we do not have any suggestions for programs that can open OCTET STREAM files. We receive hundreds of suggestions from our users every day, so suggestions for.OCTET STREAM may become available quite soon.