Stupid question , but what is a DL size envelope? Do you meen LD?
I know usually Toshiba machines above 28 copies per min don't do regular size envelopes properly. You know if you put it in the bypass and see " media Type" options at bottom of screen. Choose it and if you see envelope option beside the "thick" & "transparency" options then you can to envelopes, if not your usually beat.