Generating a contact firewall for protecting participants of a sender-controlled media (SCM) platform may include receiving an indication that a non-participant sender of the SCM platform has initiated contact with a participant recipient, using sender information associated with the contact instance to pole participants of the platform regarding a spammer status value for the sender, aggregating the spammer status values, and, based on a comparison of the aggregated spammer status values with a spammer threshold, causing future contacts from the sender to be rejected by the platform. Similar techniques may be implemented for generating a contact firewall for protecting members of a call group.