Reputation is not a single published score; each mailbox provider maintains its own internal signal, built continuously from delivery outcomes: bounce rates, spam complaints, engagement (opens, replies, deletions without reading), and authentication pass rates.
Reputation is tracked at both the IP and domain level, and increasingly domain reputation matters more as providers get better at IP-agnostic evaluation. A clean new IP paired with a poor-reputation domain still lands in spam.
Reputation recovers slowly and degrades quickly: a single bad send to a purchased or stale list can undo weeks of careful warm-up. This is the core reason PulsePigeon isolates transactional and marketing traffic onto separate lanes.