What Is An Octet Stream
The answer here is: It depends. If I wrote it, it could range from malfunctioning to accidentally dangerous. The issue here is the rouce of the attachment. If i send you a binary file, say and.exe it will probably be encoded that way. Since I'm a nice guy it probably won't hurt anything.
The primary subtype, 'octet-stream', is to be used in the case of uninterpreted binary data, in which case the simplest recommended action is to offer to write the information into a file for the user. Two additional subtypes, 'ODA' and 'PostScript', are defined for transporting ODA and PostScript documents in bodies.
Because of their use by malicous folks,.zip files have been blocked at our symantec firwall at work. I know of know way of doing that with the standard Linux firewall. You can go out and get a tool that plugs into sendmail and scans attachments and strips them out of the email. If you look at an actual email, with an attachment, say in /var/mail/username a binary attachment is just going to be a bunch of unreadable characters.
Octet Stream Viewer
What Is Application/octet-stream Content Type
Its possible to write a little job that would find binary attachments and replace them with a notice saying the file was stripped out. Its probably a while read -r rr do done type loop.