Telemetry

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mailglass emits standard :telemetry spans on every entry point — delivery, rendering, webhook ingest, and reconciliation.

Prerequisites

  • telemetry dependency available (installed by default)
  • An event handler attached to :mailglass events

Available Spans

The following spans include [ID, :start | :stop | :exception] events:

  • [:mailglass, :deliver] — synchronous delivery pipeline
  • [:mailglass, :render] — render pipeline (HEEx to HTML/Text)
  • [:mailglass, :webhook, :ingest] — webhook verification and ingest
  • [:mailglass, :reconcile] — delivery status reconciliation

PII Whitelist

Telemetry metadata includes:

  • tenant_id
  • message_id
  • stream (e.g. transactional)
  • adapter
  • status
  • latency

It never includes recipient addresses, subject lines, or message bodies.

Example: Logging delivery latency

:telemetry.attach(
  "log-delivery",
  [:mailglass, :deliver, :stop],
  fn _name, measurements, metadata, _config ->
    Logger.info("Delivered message #{metadata.message_id} in #{measurements.duration}ms")
  end,
  nil
)

End-to-End Example

:telemetry.attach(
  "test-telemetry",
  [:mailglass, :render, :stop],
  fn _name, _measurements, metadata, _config ->
    send(self(), {:telemetry_rendered, metadata.function})
  end,
  nil
)

MyApp.UserMailer.welcome(%{email: "alice@example.com"})
|> Mailglass.Renderer.render()

assert_receive {:telemetry_rendered, :welcome}