How do I send transactional emails from an API?

Sending transactional emails from an API boils down to: pick a provider, verify your domain, get an API key, then make a single authenticated POST request with the recipient, subject, and content (or template ID + variables).

Minimal step-by-step

1. Choose a transactional email provider
   Examples: Resend, Postmark, SendGrid, Mailgun, Amazon SES, Mailtrap, Brevo, Notify, etc. All expose a REST/HTTPS API for sending.

2. Verify your sending domain

   • In the provider’s dashboard, add your domain (e.g., yourapp.com).
   • Add the DNS records they give you (SPF, DKIM, and usually DMARC).
   • Wait for the domain status to show “verified.” This lets you send from addresses like noreply@yourapp.com and improves deliverability.

3. Create an API key

   • Generate an API key in the dashboard.
   • Store it securely as an environment variable (e.g., EMAIL_API_KEY) instead of hardcoding it.

4. Call the send endpoint from your backend
   The exact URL and fields vary by provider, but the pattern is the same: an authenticated POST with JSON.

   Generic example:

   POST [https://api.provider.com/v1/emails](https://api.provider.com/v1/emails)
   Authorization: Bearer YOUR_API_KEY
   Content-Type: application/json
   
   {
     "from": "Your App <noreply@yourapp.com>",
     "to": "user@example.com",
     "subject": "Your password reset",
     "html": "<p>Click to reset your password: <a href=\"[https://yourapp.com/reset?token=ABC123](https://yourapp.com/reset?token=ABC123)\">Reset password</a></p>",
     "text": "Click to reset your password: [https://yourapp.com/reset?token=ABC123](https://yourapp.com/reset?token=ABC123)"
   }
   

   Or using a template:

   POST [https://api.provider.com/v1/emails](https://api.provider.com/v1/emails)
   Authorization: Bearer YOUR_API_KEY
   Content-Type: application/json
   
   {
     "from": "Your App <noreply@yourapp.com>",
     "to": "user@example.com",
     "template_id": "password-reset-v1",
     "variables": {
       "reset_url": "[https://yourapp.com/reset?token=ABC123](https://yourapp.com/reset?token=ABC123)"
     }
   }
   

5. Handle errors and logs

   • Check the HTTP status and error body from the API response.
   • Use the provider’s dashboard logs and/or webhooks to confirm delivery, detect bounces, and debug issues.

Example with a specific provider (Resend-style)

In a Node/Next.js backend:

const res = await fetch("https://api.resend.com/emails", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.RESEND_API_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    from: "Your App <hello@yourapp.com>",
    to: "user@example.com",
    subject: "Welcome to Your App",
    html: "<h1>Welcome!</h1><p>Thanks for signing up.</p>",
  }),
});

const data = await res.json();
if (!res.ok) {
  throw new Error(`Send failed: ${JSON.stringify(data)}`);
}

The same idea applies in Python, Ruby, Go, etc., using either raw HTTP or the provider’s SDK.

If you tell me your stack and which provider you’re considering, I can give a tailored snippet and setup checklist.