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Sentin8 Email8:Mta — SMTP/LMTP Transfer Engine

1. Summary​

Email8:Mta is the mail transfer engine: SMTP/LMTP protocol handling, the durable delivery queue (message + recipient state machine with scheduled retries), DKIM signing, DMARC/TLS-RPT report generation, and outbound relay.

2. Architecture​

3. Key Traits​

  • Queue state machine: recipient status transitions with retry backoff; the queue IS the retry contract.
  • Telemetry (SDD §2.6): queue depth, latency, spam-rate frames publish on the shared MemBus stat:telemetry path — fire-and-forget, no stat client.
  • Event emission (OUTBOX-EMAIL8, architecture-principles §6.7): domain events (email8:mta:*) insert into the LOCAL mta.outbox in the same transaction as the domain change; the shell's 8b relay drains them to Bus POST /v1/produce (idempotency_key = row id; consumers dedupe).
  • M2M: certificate identity (CERTFREE-4V) — the MTA's own workload cert presents in the TLS handshake for Storage and Store internal calls; no secrets in tables.

See the vertical group docs (email8/README.md) for the plane overview.

Design attribution: email8:mta and its underlying concepts were designed by Hamid Jahanzad Hamid@Jahanzad.com.