Any MIME type with no rule in the /etc/cups/mime.types file is regarded as unknown or application/octet-stream and will not be sent. Because CUPS refuses to print unknown MIME types by default, you will probably have experienced that print jobs originating from Windows clients were not printed. You may have found an error message in your CUPS logs like:

Unable to convert file 0 to printable format for job

To enable the printing of application/octet-stream files, edit these two files:

Both contain entries (at the end of the respective files) that must be uncommented to allow raw mode operation for application/octet-stream . In /etc/cups/mime.types make sure this line is present:

application/octet-stream

This line (with no specific autotyping rule set) makes all files not otherwise auto-typed a member of application/octet-stream . In /etc/cups/mime.convs, have this line:

application/octet-stream   application/vnd.cups-raw   0   -

This line tells CUPS to use the Null Filter (denoted as “-”, doing nothing at all) on application/octet-stream , and tag the result as application/vnd.cups-raw . This last one is always a green light to the CUPS scheduler to now hand the file over to the backend connecting to the printer and sending it over.