Sender reputation
The trust score mailbox providers infer from sending behavior.
Sender reputation is shaped by authentication, complaint rate, bounce rate, engagement, spam trap hits, sending consistency, and infrastructure history. It exists at multiple levels: domain, IP, envelope sender, and sometimes individual mailbox.
reading this as teams building autonomous agents
An agent stack treats email as a two-way primitive. Inbound has to arrive as structured JSON a tool call can consume, sends have to be safe to retry when a model loop repeats itself, and every action needs an audit trail. A provider without inbound parsing only solves half the problem.
Applied to sender reputation, that means weighing inbound parsing, idempotency keys, webhook coverage, and operating track record ahead of the rest, against inbound parsing into tool calls and model-generated sends that must not duplicate.