Rewrite as a Rust, Apache-2.0 workspace

Supersedes the Go + embed-Mox design. The Go tree is removed; its
architecture doc is preserved at docs/archive/ARCHITECTURE-go-embed-mox.md
because its competitive analysis and data model still hold.

Five decisions recorded as ADRs:

  0001  Rust, not Go — accepting ~5,500 lines of protocol code that Mox
        would have given us free, to get the first permissively licensed
        Rust mail server. Costs stated plainly.
  0002  Apache-2.0, not MIT or AGPL — patent grant, trademark, CLA-free
        contribution. Public on GitHub; Gitea stays as the private fallback.
  0003  Stalwart's primitive crates (Apache-2.0/MIT) yes; its AGPL server
        crates never. DANE and MTA-STS sit on the AGPL side of that line,
        which is why we write our own.
  0004  Milestones, reordered: embedded inbound is required at launch.
  0005  Oracle Cloud blocks outbound :25, so direct-to-MX is impossible on
        the launch host. Split delivery is mandatory, not an on-ramp.

Twelve crates in three tiers. Tier 1 (mail-dane, mail-mta-sts, mail-dsn)
is standalone and publishable — no `dane` or `mta-sts` crate exists on
crates.io at all today.

openmail-relay ships the provider table as data, with SES and Oracle from
the start. Oracle's and Resend's SPF includes are deliberately None: a
guessed include turns the DNS check green against a mechanism the provider
does not honour, and mail still fails SPF silently.

cargo check/test/clippy/fmt all green; unsafe_code is forbidden workspace
wide; cargo-deny enforces the licence policy in CI.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JkyvfNJGTshJNE9FtwPLk7

docs/adr/0004-milestones.md

@@ -0,0 +1,51 @@
+# ADR 0004 — Milestones
+
+**Status:** Accepted, 2026-09-02.
+
+Reordered from the archived Go plan. The original put embedded inbound at
+milestone 4 and treated it as optional-until-later; ADR 0005 makes it
+**required at launch**, because the launch host cannot send direct-to-MX at all.
+
+## v0.1 — the agent layer, provable without mail
+
+Nothing here needs a working mail server, which is the point: it is all
+testable in CI.
+
+- [x] Apache-2.0 workspace, 12 crates, `cargo check` green
+- [x] `openmail-relay` provider table (SES, Oracle, SendGrid, Postmark, Resend, custom)
+- [ ] `openmail-core::extract::strip_quoted` — the first real algorithm
+- [ ] `openmail-core::thread` resolution, both bases
+- [ ] `openmail-store` — Postgres schema, embedded migrations, S3 blobs
+- [ ] `openmail-api` — v0 REST, bearer auth
+- [ ] Ingest endpoint: POST a raw `.eml` and get a threaded, extracted message
+      back. Closes the loop with **zero mail infrastructure.**
+
+## v0.2 — receive
+
+- [ ] `openmail-smtpd` on :25, real MX for a test domain
+- [ ] `openmail-guard` gate, `mail-auth` SPF/DKIM/DMARC verdicts recorded
+- [ ] `openmail-junk` scoring
+- [ ] `message.received` webhooks + WebSocket
+
+## v0.3 — send, and the MCP surface
+
+- [ ] Relay send via SES and Oracle, DKIM-signed locally
+- [ ] `mail-dsn` bounce handling wired to outbox state
+- [ ] `openmail-mcp` — an agent creates an inbox, receives, and replies, alone
+
+## v0.4 — direct-to-MX, and the crates ship
+
+- [ ] `mail-dane` and `mail-mta-sts` complete, **published to crates.io**
+- [ ] Direct MX delivery with both enforced
+- [ ] IP warmup, FBL enrolment, suppression lists
+
+## v1.0
+
+- [ ] IMAP front-end so humans use their own client against the same mailbox
+- [ ] Multi-tenancy beyond `pods`
+- [ ] Deliverability track record worth publishing
+
+## Not in v1
+
+A hosted SaaS, billing, or a webmail UI. `pods` exists so the SaaS path stays
+open architecturally — do not remove it as unused.