MTA-STS
A policy that tells mail servers to require TLS for inbound delivery.
Mail Transfer Agent Strict Transport Security lets a domain publish a policy requiring encrypted SMTP connections from supporting senders. It helps prevent downgrade attacks where delivery falls back to unencrypted transport.
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 mta-sts, 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.