I am working on a project where I need to send requests over email instead of http,
to prevent email servers or clients from messing with the body (especially urls) I have set the Content-Type header in my SMTP request to application/octet-stream instead of text/plain.
The content however is actually plain text so I also specified ;charset=UTF-8.
Looking at RFC it seems that the charset parameter is only allowed for text/* types, however I also found many examples where charset was used with application/* types.
Now I wonder, is application/octet-stream; charset=UTF-8 a valid MIME type?
As the application/octet-stream definition (IANA-RFC) doesn't define a charset for this applicationtype and the definition for application/json (IANA-RFC) a mimetype thats used more often includes a note:
No "charset" parameter is defined for this registration.
Adding one really has no effect on compliant recipients.
I would strongly recommend to assume that the statement not only applies in this special case, but also in other application/* which have no charset defined.
So I can't say if it is valid to pass parameters that aren't defined, but the RFC clearly implies that the charset parameter for application/octet-stream (and other application/* that do not define charset) has no effect.