DMARC
A policy that tells mailbox providers what to do when SPF or DKIM fail.
DMARC is a DNS TXT record that publishes a policy (none, quarantine, reject) and a reporting address. Google and Yahoos February 2024 bulk-sender requirements made DMARC mandatory at scale. Start with p=none, monitor reports for several weeks, then tighten.
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 dmarc, 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.