opensender

Deploy an instance · Send email · Stay up to date · Operations · Development

opensender

A self-hosted email platform that speaks the Resend API. Deploy it into your own AWS account and point any official Resend SDK at it: the only thing that changes in your app is the base URL.

• Drop-in API. Emails, batch, scheduling, idempotency, domains, API keys, contacts, segments, broadcasts, webhooks and inbound, matching Resend's wire format.
• Runs on your AWS. SES v2, Lambda, DynamoDB and CloudFront, deployed with SST. No third-party email vendor, and your data stays in your account.
• Multi-tenant. Each team gets its own SES tenant, plan quotas, and reputation guardrails that freeze a team before it can hurt the account.
• Dashboard included. Domains, keys, emails, broadcasts, webhooks and team members, plus OAuth for connected apps and an MCP server for agents.
• Cheap to run. Serverless pay-per-use, native CloudWatch observability, budgets and a weekly cost report.

Quickstart

git clone https://github.com/teovillanueva/opensender my-mailing
cd my-mailing
# edit instance.config.ts: domain, region, alert email, plans
pnpm install
pnpm exec sst deploy --stage production

The full walkthrough, including DNS, secrets and the first admin user, is in Deploying an instance.

Send your first email

Use the official Resend SDK and set the base URL to your instance's API:

import { Resend } from "resend";

const resend = new Resend("re_123456789", {
  baseUrl: "https://api.mailing.example.com",
});

const { data, error } = await resend.emails.send({
  from: "hello@example.com",
  to: "delivered@example.com",
  subject: "Hello World",
  html: "<strong>it works!</strong>",
});

Or with plain HTTP:

curl -X POST https://api.mailing.example.com/emails \
  -H "Authorization: Bearer re_123456789" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "hello@example.com",
    "to": "delivered@example.com",
    "subject": "Hello World",
    "html": "<strong>it works!</strong>"
  }'

More in Sending email.

Documentation

Guide	What's in it
Deploying an instance	Prerequisites, configuration, DNS, secrets, first admin, one-time AWS setup
Sending email	SDKs, base URL, API keys, request limits
Keeping an instance up to date	Private instance repos, hourly upstream sync, SST Console Autodeploy
Operations	Observability, SES limits, secret rotation, DLQs, paused tenants, costs
Development	Repo layout, checks, local dev, acceptance suite
Glossary	Instance, Team, Tenant, Plan and the rest of the domain language
Architecture decisions	ADRs
Specification	The full product and engineering spec

License

MIT