Documentation

Everything, stated precisely.

Start with the quickstart — it ends by having you read a real trace, which is the only part of this product that needs explaining.

Quickstart API reference

POST /api/v1/emails

# Send a transactional email
curl -X POST https://app.getoutsend.com/api/v1/emails \
  -H "Authorization: Bearer $OUTSEND_API_KEY" \
  -H "Idempotency-Key: order-8421" \
  -d '{
    "from": "Acme <hello@mail.acme.com>",
    "to": ["maya@example.com"],
    "reply_to": "support@acme.com",
    "subject": "Your order is on its way",
    "html": "<p>Hi Maya, it shipped!</p>"
  }'

await fetch('https://app.getoutsend.com/api/v1/emails', {
  method: 'POST',
  headers: {
    Authorization: `Bearer ${process.env.OUTSEND_API_KEY}`,
    'Content-Type': 'application/json',
    'Idempotency-Key': 'order-8421',
  },
  body: JSON.stringify({
    from: 'Acme <hello@mail.acme.com>',
    to: ['maya@example.com'],
    subject: 'Your order is on its way',
    html: '<p>Hi Maya, it shipped!</p>',
  }),
});

# Any SMTP client or framework mailer
Host      smtp.getoutsend.com
Port      2587
Security  STARTTLS
Password  your OutSend API key

# Keys can be limited to a single sending domain

Start

Send your first message and read what it left behind.

Quickstart

Verify a domain, send your first message, and read the trace it leaves behind — in about ten minutes.

Reference

Every field, event, and limit, stated precisely.

API reference

The sending endpoint, its fields, its errors, and the limits that apply to it.

SMTP relay

Point any existing mailer at OutSend and change nothing else about your application.

Webhooks

Get events pushed to you as they happen, signed so you can prove they came from us.

Events reference

All eight event types, what each one means, and what evidence comes with it.

CLI

Set up, inspect, replay, and diagnose OutSend from a shell script, a runbook, or a CI job.

MCP server

Give an agent the ability to send, inspect, explain, and remediate email — with evidence attached and approval gates on anything consequential.

Guides

DNS, deliverability, and running it yourself.

Domains and DNS

What DKIM, SPF, and DMARC actually do, how to publish them, and how to tell when one is wrong.

Self-hosting

Run the open core on your own infrastructure, with your own AWS account, in about five minutes.

Migrating

Field maps and checklists for leaving your current provider.

From SendGrid

Field mapping, webhook equivalents, and a migration checklist for moving off SendGrid.

From Mailgun

Field mapping, webhook equivalents, and a migration checklist for moving off Mailgun.

From Amazon SES

Keep SES underneath, gain the control plane you were about to build yourself.

From Postmark

A close API shape, a similar streams model, and what actually differs.

From Resend

A near-identical API shape, plus the parts that are deliberately different.

Something here wrong or missing?

The docs live in the repo. Corrections are welcome and we publish them.

Edit on GitHub