What unique signals do Gmail track (engagement, recency, machine learning)?

Gmail tracks extensive engagement signals:

Open behavior: Who opens, how quickly, how often.

Click patterns: Link engagement and frequency.

Replies: Strong positive signal. Conversational engagement.

Time-to-action: How quickly users interact after receiving.

Folder management: Moving to/from spam, starring, archiving.

Recency weighting: Recent behavior matters more than old behavior.

ML prediction: Models predict whether each user will want each message based on all signals.

Gmail builds individual user models that shape placement per recipient.

Gmail remembers everything about your relationship with each recipient.