What signals do Gmail and Yahoo share publicly (Postmaster, FBL)?;

Gmail Postmaster Tools provides visibility into your sending reputation at Google, showing domain reputation (bad, low, medium, high), IP reputation, spam rate, authentication results, and delivery errors.

Yahoo Complaint Feedback Loop sends notifications when users mark your mail as spam. This provides complaint data you can use for list hygiene and monitoring.

Gmail does not offer a traditional FBL. You cannot receive individual complaint notifications from Gmail users. Postmaster Tools shows aggregate spam rates instead.

Both providers publish postmaster documentation explaining their requirements and best practices.

Neither provider shares complete filtering details. The signals they provide are helpful but incomplete. You see outcomes more than causes.

Public signals are glimpses through the window. They reveal important information without showing the entire picture.