Crate mailrs_outbound_queue 

Outbound mail queue primitives: DKIM signing, DSN generation, MTA-STS lookup, retry/backoff, plus a pluggable store trait and a Postgres reference implementation.

mailrs-outbound-queue extracts the queue + delivery layer from mailrs so it can be reused — or driven by a custom store — in any Rust MTA. The “pure” pieces (dkim_sign, dsn, mta_sts, retry) depend only on hashes / DNS / pure arithmetic; the QueueStore + Notifier traits in store decouple delivery state from any particular backend.

Feature flags

Feature	Default	Includes
pg	on	PgQueueStore + RedisNotifier + the bundled DeliveryWorker that consumes them. Pulls in sqlx and redis.

Disable the pg feature if you want only the traits + pure primitives:

mailrs-outbound-queue = { version = "1", default-features = false }

Two paths

The crate exposes two parallel APIs against the same underlying queue semantics:

• Trait API (QueueStore, Notifier) — the portable surface. Use this if you want a non-PG backend, or if you want your own delivery loop. An always-available InMemoryQueueStore is included for tests + pilots.
• PG free functions in the queue module — convenience for the common case where you already have a sqlx::PgPool and just want queue::enqueue(pool, ...). These back the bundled DeliveryWorker and are what mailrs itself uses.

Both APIs are stable for v1.x and back-compatible. The trait API plus a generic worker is the target for v2.

Re-exports

pub use dkim_sign::DkimSignConfig;

pub use queue::QueueStatus;

pub use queue::QueuedMessage;

pub use retry::retry_delay_secs;

pub use retry::retry_delay_secs_jittered;

pub use retry::should_bounce;

pub use store::InMemoryNotifier;

pub use store::InMemoryQueueStore;

pub use store::NoopNotifier;

pub use store::Notifier;

pub use store::QueueStore;

pub use store::StoreError;

pub use pg_store::PgQueueStore;

pub use pg_store::RedisNotifier;

pub use worker::DeliveryWorker;

pub use worker::WorkerConfig;

pub use worker::group_by_domain;

Modules

dkim_sign

DKIM signing helpers (RFC 6376): config + sign-and-prepend.

dsn

Delivery Status Notification (RFC 3464) formatting.

mta_sts

MTA-STS (RFC 8461) policy lookup + caching.

pg_store

Postgres-backed QueueStore implementation (feature-gated). Postgres / Redis-backed implementations of QueueStore and Notifier.

queue

Queue row type, status enum, and retry-attempt bookkeeping.

retry

Exponential-backoff retry math + “is it permanent?” classifier. Exponential-backoff retry helpers for SMTP outbound delivery.

store

Pluggable QueueStore trait + an in-memory reference impl. Storage abstractions for the outbound queue.

worker

Async delivery worker that drains the queue + dispatches via SMTP (feature-gated).

Enums

DeliveryEvent

Outbound delivery event for external observers (admin UI, audit log, metrics pipeline, TLSRPT reporter).

TlsAttemptOutcome

Outcome of one STARTTLS attempt, carried by DeliveryEvent::TlsAttempt. The four variants discriminate between TLS success, server-side refusal (still safely usable in plain), and handshake failure (with the structured mailrs_smtp_client::TlsOutcome underneath).

Type Aliases

DeliveryEventSender

Callback channel for DeliveryEvent notifications. Wrapped in Arc so the worker can clone it across spawned delivery tasks.