IDX policy gives MLS participants the ability to authorize limited electronic display of their listings by other participants. MLSs are required to promptly provide. Tools and Support; > Internet Data Exchange (IDX). About IDX. IDXLogo_ Internet Data Exchange or IDX is also referred to as Broker Reciprocity. What is IDX? IDX stands for Internet Data Exchange. IDX is a cooperative service offered by Realcomp II Ltd. through which participating.