Suppressions
A list of recipients the provider refuses to send to.
Suppression lists hold addresses that bounced, complained, or unsubscribed. Most providers manage suppressions automatically and refuse to send to suppressed addresses. Some let you import or export the list; treating suppressions as authoritative protects sender reputation.
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 suppressions, 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.