Sender reputation

Sender reputation is the running judgement each mailbox provider forms about your sending identity, based mostly on how recipients behave: opens and replies on one side, complaints, deletions without reading and spam-trap hits on the other. It decides whether mail reaches the inbox, a secondary tab or nowhere. Reputation attaches to both the IP and the domain, and the domain side is the stickier of the two, so moving to a new IP rarely fixes a list problem.