Some receiving providers operate feedback mechanisms that let qualified senders learn when recipients report messages as spam.
Implementations differ. A feedback loop might provide message-related data, aggregate information, or provider-specific dashboards.
What to do with it
Complaint data should feed suppression and root-cause analysis. Look for the campaign, list source and process that produced unwanted mail.
Do not assume every provider offers the same feedback mechanism, and do not confuse a complaint feed with a universal reputation score.