Complaint rate
The share of recipients who mark email as spam.
Complaint rate is one of the strongest negative sender reputation signals. It is usually measured as spam complaints divided by delivered messages. High complaint rates often mean poor consent, misleading subject lines, stale lists, or irrelevant targeting.
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 complaint rate, 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.