As stated by the NAR, "All listings displayed pursuant to IDX shall identify the listing firm, and the email or phone number provided by the listing participant in a reasonably prominent location and in a readily visible color and typeface not smaller than the median used in the display of listing data."
The Listing Broker Attribution field is notated in the office record, which must be updated by the office's Managing Broker. This can be accessed using MIBOR Central at member.mibor.com.
The current default is to present the Listing Agent Email address.