---
name: postshiba
description: Send transactional email from an app or a SaaS platform through the PostShiba HTTP API, SMTP, or MCP. Use this for per-customer domains and tenants, opt-in newsletters and campaigns, agent inboxes, and signed webhooks. Never for cold email or outreach.
---

# PostShiba

PostShiba is an email API for apps and SaaS platforms. You send transactional and marketing mail over HTTP or SMTP, receive it in inboxes, and read delivery through signed webhooks.

## When to use it

Use PostShiba for a transactional email API, a platform that sends on each customer's domain through tenants, agent inboxes with signed webhooks, or an SMTP relay for your app or a self-hosted newsletter tool.

Opt-in marketing email is welcome: newsletters and campaigns to people who signed up, on a Marketing cluster, including from self-hosted tools like Mautic or listmonk over SMTP. Cold email, outreach, and bought, rented, or scraped lists are banned. The full rules are at https://www.postshiba.com/use-cases.

## Sign up and get ready to send

Anyone can sign up self-serve. Once your first cluster and domain are ready, you can send to your own team's addresses. External recipients need production approval, which we review by hand and is usually quick.

1. Sign up at https://app.postshiba.com/users/sign_up and confirm your email address.
2. In the dashboard, add a payment method.
3. Create your first cluster. It starts the 7-day free trial. See [Clusters](/docs/dashboard/clusters/introduction.md).
4. Add a sending domain and verify its DNS records. See [Add a domain](/docs/add-a-domain.md).
5. Create an API key. A Send only key can send mail. See [Create an API key](/docs/create-an-api-key.md).

## Send the first email

POST JSON to `/api/v1/emails` with a Bearer token. `from` must be an address on a verified sending domain. Until the team has a cluster that is ready to send, this returns `403` with `cluster_not_ready`.

```bash
curl -sS -X POST \
  -H 'Authorization: Bearer YOUR_API_KEY' \
  -H 'Content-Type: application/json' \
  -d '{
    "from": "hello@mail.example.com",
    "to": ["you@example.com"],
    "subject": "Your receipt",
    "text": "Thanks for your order.",
    "html": "<p>Thanks for your order.</p>"
  }' \
  https://app.postshiba.com/api/v1/emails
```

A queued send returns `201 Created`.

## MCP

The MCP server is `https://app.postshiba.com/mcp`. Send the same API key as `Authorization: Bearer YOUR_API_KEY`. Client setup is in [Connect MCP](/docs/connect-mcp.md).

## More

- Docs index: [/llms.txt](/llms.txt)
- OpenAPI: [/openapi.json](/openapi.json) and [/api/v1/openapi.yaml](/api/v1/openapi.yaml)
- Auth: [/auth.md](/auth.md) and [/docs/create-an-api-key.md](/docs/create-an-api-key.md)