// for engineers

The email API
you'd actually pick.

Typed SDKs in 7 languages. Idempotent sends. HMAC-signed webhooks with replay. OpenTelemetry-compatible tracing. Zero proprietary dashboards required to ship.

Read the docs →Browse SDKs

SDK languages

Median send

187ms

Event types

Idempotency TTL

24h

// send

One endpoint.
Every send shape.

Transactional, marketing, receipts, one-offs, bulk batch, React components rendered at send time — the same POST /v1/email handles all of it.

Idempotency keys
Every key cached for 24h. Retry a thousand times, deliver exactly once.
Batch sending
Up to 100 recipients per request, individually tracked, single atomic call.
Scheduled delivery
Pass scheduled_at; we queue and fire to the minute.
Attachments up to 40MB
base64 or pre-signed URL, MIME types you pick.
Tags & metadata
Up to 10 tags, 40 metadata fields. Filter logs, slice analytics.

POST /v1/email

// One call. Typed response. Retries built in.
const { id, status } = await volt.send({
  from:    'team@acme.dev',
  to:      ['dev@customer.io'],
  subject: 'Your receipt #4827',
  react:   <Receipt order={order} />,
  tags:    ['billing', 'receipt'],
  metadata: { order_id: order.id, plan: 'pro_plus' },
  idempotencyKey: `receipt:${order.id}`,
});
 
// → { id: "em_01HQ7X9KVZT…", status: "queued" }

// events & webhooks

Every state change,
signed and streamed.

Delivered · Opened · Clicked · Bounced · Complained · Deferred · Unsubscribed · Queued · Rejected. Nine event types, HMAC-signed payloads, exponential retry, dashboard replay.

HMAC-SHA256 signing
Verify X-VoltMail-Signature; rotate secrets without downtime.
Retry with backoff
5 attempts over 3 hours, then dead-letter queue you can replay.
Replay from dashboard
Pick a date range, pick events, replay to any endpoint.
Event filtering
Subscribe per-endpoint to only the events you need. No noise.
TypeScript schemas
Zod-validated payloads bundled with the SDK.

events — livestreaming

deliveredteam@acme.dev → ops@cargodrop.ioem_01HQ7XD88LG

unsublist-unsub · one-clickem_01HQ7XAB2MN

bouncedsmtp 550 5.1.1 · user unknownem_01HQ7XBPQ4S

complainedabuse@aol.com · feedback loopem_01HQ7XE4K1J

deferredsmtp 451 · greylistem_01HQ7XCFD2W

deliveredteam@acme.dev → ana@peddlebee.coem_01HQ7XAB2MN

clickedhttps://acme.dev/r/4827302

openedbeacon · em_01HQ7X9KVZT204

// api keys

Scoped keys.
Zero-downtime rotation.

Separate live from test. Separate read from send. Rotate without a deploy. Audit who used what, last.

Permission scopes
send:write, logs:read, domains:admin, etc.
IP allowlists
Bind a key to specific CIDR ranges.
Rate limits per key
Protect production from runaway scripts.
Last-used tracking
Find stale keys. Revoke with a click.
Audit log
Every key action (create, rotate, revoke) recorded, exportable as CSV.

dashboard — api keys

prod-apiLIVEsend:writevm_live_•••••• 7a2f
prod-logsLIVElogs:readvm_live_•••••• 3c91
ci-testsTESTsend:writevm_test_•••••• b4e2
webhooks-adminLIVEwebhooks:adminvm_live_•••••• 9d05
legacy-migrationREVOKEDvm_live_•••••• e118

5 active · 1 revoked · rotated 12d ago

// in the box

What ships with every SDK.

Typed client

Full request + response types per endpoint, generated from OpenAPI.

Discriminated errors

`InvalidInputError`, `RateLimitError`, `IdempotentReplay` — never `unknown`.

Retry policy

Exponential backoff with jitter on 5xx + network errors. Configurable.

Webhook verifier

HMAC-SHA256 signature check, replay-window guard, raw-body helper.

Zod schemas

Every event type bundled. Parse webhook bodies with one call.

Mock client for tests

In-memory implementation that records sends, asserts, and replays.

Tracing hooks

OpenTelemetry-compatible. Wire to your existing trace context.

CLI

Tail logs, send a test email, verify a domain — without the dashboard.

Read the OpenAPI.
Paste the key. Ship.

Free forever up to 3,000 emails / month. No card. No call. The pricing page is the contract.

Start free →Compare plans

The email APIyou'd actually pick.

One endpoint.Every send shape.

Every state change,signed and streamed.