I have a Zebra GK420d connect to OS X via CUPS. However, when I send files to it that are written in ZPL or EPL they are only printed in plain text.
Am I required to change to mode on the printer?
Contrary to what others said, you don't need to specially add a raw queue.
Instead, you can submit raw files into any queue using -o raw
switch:
lpr -P CupsPrinterName -o raw path/to/label.zpl
Printer name can be found over that link in CUPS:
http://localhost:631/printers/
This also works on other platforms that use CUPS, like Linux.