Mailglass

Mail you can see through.

Mailglass is a batteries-included transactional email framework for Phoenix. It composes on top of Swoosh and ships the framework layer Swoosh deliberately leaves out: HEEx-native components with Outlook MSO/VML fallbacks, a LiveView preview/admin dashboard, normalized webhook events, an append-only event ledger with Postgres trigger immutability, multi-tenant routing, message streams, RFC 8058 List-Unsubscribe with signed tokens, suppression lists, and webhook-driven auto-suppression.

It is shipped as three sibling packages: mailglass (core), mailglass_admin (mountable LiveView dashboard), and mailglass_inbound (inbound routing; v0.5+). It is for senior Phoenix teams building production transactional email — welcome flows, password resets, magic links, receipts, notifications — who today rebuild the same 40% of framework plumbing on every project.

Requirements

• Elixir ~> 1.18 and OTP 27+
• Phoenix ~> 1.8
• Phoenix LiveView ~> 1.1
• Ecto / Ecto SQL ~> 3.13
• PostgreSQL 14+ (trigger support required; citext used for case-insensitive address match)
• Swoosh ~> 1.25 (compose any Swoosh adapter for transport)

Installation

Add mailglass to your dependencies:

# mix.exs
def deps do
  [
    {:mailglass, "~> 0.3"},
    {:mailglass_admin, "~> 0.3", only: [:dev]}
  ]
end

Fetch deps, run the installer, and migrate:

mix deps.get
mix mailglass.install
mix ecto.migrate

The installer generates: a MyApp.Mailing context, the three-table migration (mailglass_deliveries, mailglass_events, mailglass_suppressions plus the immutability trigger), router mounts for the dev preview and webhook plug, a default mailable and layout, an Oban worker stub (when Oban is installed), and a config/runtime.exs configuration block.

Quickstart

Run the full onboarding path first:

mix deps.get
mix mailglass.install
mix ecto.migrate
mix compile

Define a mailable:

defmodule MyApp.UserMailer do
  use Mailglass.Mailable, stream: :transactional

  def welcome(user) do
    new()
    |> to(user.email)
    |> from({"MyApp", "support@example.com"})
    |> subject("Welcome to MyApp")
    |> html_body("<h1>Welcome to MyApp</h1>")
    |> text_body("Welcome to MyApp")
    |> Mailglass.Message.put_function(:welcome)
  end
end

Send it — synchronously, asynchronously (via Oban when available), or in a batch:

MyApp.UserMailer.welcome(user) |> Mailglass.deliver()
MyApp.UserMailer.welcome(user) |> Mailglass.deliver_later()
Mailglass.deliver_many(Enum.map(users, &MyApp.UserMailer.welcome/1))

Preview mailables in dev at http://localhost:4000/dev/mail — sidebar of discovered mailables, device width and dark-mode toggles, HTML/Text/Raw/Headers tabs, live-editable assigns.

Feature highlights

• HEEx-native components (container, section, row, column, heading, text, button, img, link, hr, preheader) with MSO VML fallbacks for Outlook. No Node toolchain.
• Pure render pipeline — HEEx → Premailex CSS inlining → data-mg-* strip → auto-plaintext via Floki walker. ~4ms on a ten-component template.
• Append-only event ledger — mailglass_events table protected by a Postgres trigger that raises SQLSTATE 45A01 on UPDATE/DELETE.
• Native mailable setters — Mailglass.Message.to/2, from/2, subject/2, html_body/2, text_body/2, header/3, attach/2, and put_tag/2 keep the common path free of direct Swoosh.Email.* calls while update_swoosh/2 remains the escape hatch.
• Stream-aware deliverability — :transactional, :operational, and :bulk are enforced message streams. RFC 8058 one-click unsubscribe headers are injected automatically for :bulk and can be opted into on :operational.
• Idempotency — partial UNIQUE index on idempotency_key WHERE idempotency_key IS NOT NULL; replay-safe webhooks and delivery retries.
• Multi-tenant from day one — tenant_id on every record, Mailglass.Tenancy behaviour, SingleTenant default resolver, and an Oban tenancy middleware (conditionally compiled).
• Fake adapter as the release gate — deterministic, in-memory, time-advanceable; merge-blocking in CI so the full pipeline is testable without real provider credentials.
• Swoosh as transport — compose on any Swoosh adapter (Postmark, SendGrid, Mailgun, SES, Resend, local SMTP, etc.).
• Normalized webhook events — Anymail event taxonomy verbatim (queued, sent, bounced, delivered, opened, clicked, complained, unsubscribed, …) with reject_reason enum. Postmark, SendGrid, Mailgun, SES, and Resend are all shipped first-party providers, and matched :bounced, :complained, and :unsubscribed events project suppressions automatically.
• Test assertions — assert_mail_sent/1, last_mail/0, wait_for_mail/1, plus MailerCase, WebhookCase, AdminCase templates.
• Telemetry spans on every entry point with a PII whitelist (counts, IDs, and latencies — never addresses or bodies).
• Optional deps gated via Mailglass.OptionalDeps.*: oban, opentelemetry, mjml, gen_smtp, sigra.

Packages

Roadmap

• v0.2 — Production-credible core — native Mailglass.Message setter API, mix mailglass.upgrade.v0_2, message-stream policy, RFC 8058 unsubscribe, webhook-driven suppression projection, linked release hardening, and release-blocking Tier 1 docs.
• v0.5 — Deliverability + admin — prod-mountable admin, mix mail.doctor deliverability checks, per-tenant adapter resolver, per-domain rate limiting.
• v1.0 — API stability lock, production references, long-lived deprecation policy.

Full trajectory in .planning/ROADMAP.md and .planning/PROJECT.md.

Documentation

• guides/getting-started.md — install, route mounting, and first delivery
• guides/upgrading-from-v0_1.md — codemod-backed upgrade path for existing adopters
• guides/migration-from-swoosh.md — move from raw Swoosh to the mailglass pipeline
• guides/authoring-mailables.md — native setter API and update_swoosh/2 escape hatch
• guides/unsubscribe.md — RFC 8058 route, token, and rollout contract
• guides/dkim-setup.md — DKIM h= checks for one-click unsubscribe
• guides/webhooks.md — webhook ingest, verification, suppression, and retention

Contributing

Mailglass is developed in public. Contributor conventions, decision log, and phase-by-phase roadmap live in CLAUDE.md and .planning/PROJECT.md; a dedicated CONTRIBUTING.md lands in Phase 7.

Reproduce the default CI gate locally:

mix verify.foundation
mix verify.cold_start
mix compile --no-optional-deps --warnings-as-errors

License

MIT. The license is declared in mix.exs and applies across all sibling packages.