Documentation

Quick Start.

Send your first email with SMTPfast in under two minutes.

Overview

SMTPfast is a developer-first email API built for speed and simplicity. Send transactional emails, manage sending domains, and track delivery events through a clean REST API.

The API is compatible with Resend, so you can switch with minimal code changes.

Base URL

https://smtpfa.st/api/v1

All endpoints described in these docs are relative to this base URL.

Authentication

Every request requires a Bearer token in the Authorization header. Create an API key from your dashboard or via the API.

Header

Authorization: Bearer sf_live_your_api_key

Send Your First Email

Make a POST request to /v1/emails with the recipient, subject, and body.

Verify your sending domain first.

A send from a domain you have not verified is refused with 403 and the message Domain is not verified. Add it on the Domains page, publish the DNS records, and then come back here. The example below uses yourapp.com; replace it with a domain you own.

bash

curl -X POST https://smtpfa.st/api/v1/emails \
  -H "Authorization: Bearer sf_live_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "[email protected]",
    "to": ["[email protected]"],
    "subject": "Welcome!",
    "html": "<h1>Hello from SMTPfast!</h1>"
  }'

const res = await fetch("https://smtpfa.st/api/v1/emails", {
  method: "POST",
  headers: {
    Authorization: "Bearer sf_live_your_api_key",
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    from: "[email protected]",
    to: ["[email protected]"],
    subject: "Welcome!",
    html: "<h1>Hello from SMTPfast!</h1>",
  }),
});

const { id } = await res.json();
console.log("Sent:", id);

import requests

res = requests.post(
    "https://smtpfa.st/api/v1/emails",
    headers={
        "Authorization": "Bearer sf_live_your_api_key",
        "Content-Type": "application/json",
    },
    json={
        "from": "[email protected]",
        "to": ["[email protected]"],
        "subject": "Welcome!",
        "html": "<h1>Hello from SMTPfast!</h1>",
    },
)

data = res.json()
print("Sent:", data["id"])

Response Format

Responses are JSON, apart from exports such as /v1/contacts/export which returns CSV. A successful request returns 200, or 201 when it created something. An error carries an error field with a message that describes the issue; the HTTP status code says what kind of error it is.

Success

json

{
  "id": "email_abc123"
}

Error

json

{
  "error": "Invalid API key"
}

Next Steps

SDKs →

Official Node.js, Python, Go and PHP SDKs, and a Laravel mail driver

Authentication →

API key scopes and security

Emails API →

Send and retrieve emails

Contacts API →

Manage subscribers, properties, and segments

Broadcasts API →

Create, target, schedule, and measure campaigns

Templates API →

Write an email once with variables and send it by alias

Domains API →

Add and verify sending domains

Resend Compatibility →

Switch from Resend in minutes