Free Email API — Send Transactional Emails via REST

Need to send transactional emails from your app without setting up SendGrid, Mailgun, or AWS SES? The Agent Email Sender API lets you send plain text, HTML, and template-based emails through a simple REST endpoint. It includes 5 built-in templates, custom SMTP support, and delivery logs — all without an account or credit card.

In this guide you'll learn how to send emails via API, use built-in templates for common use cases, configure your own SMTP server, and track deliveries with the logs endpoint.

Quick Start

Get an API key (free, no signup), then send your first email in one request:

Step 1: Get an API Key

curl -X POST https://agent-gateway-kappa.vercel.app/v1/agent-email/api/keys/create

# Response:
{
  "apiKey": "em_abc123...",
  "credits": 50,
  "plan": "free"
}

Step 2: Send an Email

curl -X POST https://agent-gateway-kappa.vercel.app/v1/agent-email/api/send \
  -H "Authorization: Bearer em_abc123..." \
  -H "Content-Type: application/json" \
  -d '{
    "to": "user@example.com",
    "subject": "Order Confirmation #1234",
    "html": "<h1>Thank you!</h1><p>Your order has been confirmed.</p>"
  }'

# Response:
{
  "status": "sent",
  "email_id": "a1b2c3d4-...",
  "message_id": "<abc@mail.ethereal.email>",
  "to": ["user@example.com"],
  "subject": "Order Confirmation #1234",
  "duration_ms": 342,
  "preview_url": "https://ethereal.email/message/...",
  "note": "Using Ethereal test SMTP. Configure your own SMTP for production."
}

import requests

API_KEY = "em_abc123..."
BASE = "https://agent-gateway-kappa.vercel.app/v1/agent-email"

resp = requests.post(
    f"{BASE}/api/send",
    headers={"Authorization": f"Bearer {API_KEY}"},
    json={
        "to": "user@example.com",
        "subject": "Order Confirmation #1234",
        "html": "<h1>Thank you!</h1><p>Your order has been confirmed.</p>"
    }
)
result = resp.json()
print(result["email_id"], result["preview_url"])

const API_KEY = "em_abc123...";
const BASE = "https://agent-gateway-kappa.vercel.app/v1/agent-email";

const resp = await fetch(`${BASE}/api/send`, {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${API_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    to: "user@example.com",
    subject: "Order Confirmation #1234",
    html: "<h1>Thank you!</h1><p>Your order has been confirmed.</p>"
  })
});
const data = await resp.json();
console.log(data.email_id, data.preview_url);

The default sandbox uses Ethereal (a fake SMTP service). Every email returns a preview_url so you can see exactly what was sent — perfect for development and testing.

API Endpoints

Built-in Email Templates

Instead of writing HTML from scratch, use one of the 5 built-in templates. Just provide the template name and a variables object:

Welcome Email

curl -X POST https://agent-gateway-kappa.vercel.app/v1/agent-email/api/send/template \
  -H "Authorization: Bearer em_abc123..." \
  -H "Content-Type: application/json" \
  -d '{
    "to": "newuser@example.com",
    "subject": "Welcome to Acme!",
    "template": "welcome",
    "variables": {
      "name": "Alice",
      "message": "Your account is ready. Start building today.",
      "cta_url": "https://app.example.com/dashboard",
      "cta_text": "Open Dashboard",
      "company": "Acme Inc."
    }
  }'

Alert / Incident Email

curl -X POST https://agent-gateway-kappa.vercel.app/v1/agent-email/api/send/template \
  -H "Authorization: Bearer em_abc123..." \
  -H "Content-Type: application/json" \
  -d '{
    "to": "ops@example.com",
    "subject": "CRITICAL: Database connection pool exhausted",
    "template": "alert",
    "variables": {
      "severity": "critical",
      "title": "Database Pool Exhausted",
      "message": "Primary PostgreSQL pool reached 100% capacity at 14:32 UTC.",
      "details": "Pool: primary-db\nActive: 100/100\nWaiting: 47\nAvg wait: 12.4s"
    }
  }'

Invoice Email

curl -X POST https://agent-gateway-kappa.vercel.app/v1/agent-email/api/send/template \
  -H "Authorization: Bearer em_abc123..." \
  -H "Content-Type: application/json" \
  -d '{
    "to": "billing@client.com",
    "subject": "Invoice #INV-2026-003",
    "template": "invoice",
    "variables": {
      "invoice_id": "INV-2026-003",
      "date": "2026-03-03",
      "items": [
        {"item": "API Pro Plan (March)", "amount": "$49.00"},
        {"item": "Extra API calls (12K)", "amount": "$8.40"}
      ],
      "total": "$57.40",
      "payment_link": "https://pay.example.com/inv-003"
    }
  }'

All 5 Templates

Custom SMTP Configuration

The default sandbox is great for testing, but for production you'll want your own SMTP server. Configure it once per API key:

# Configure your SMTP server
curl -X POST https://agent-gateway-kappa.vercel.app/v1/agent-email/api/smtp/configure \
  -H "Authorization: Bearer em_abc123..." \
  -H "Content-Type: application/json" \
  -d '{
    "host": "smtp.gmail.com",
    "port": 587,
    "secure": false,
    "user": "yourname@gmail.com",
    "pass": "your-app-password"
  }'

# Verify the connection
curl -X POST https://agent-gateway-kappa.vercel.app/v1/agent-email/api/smtp/verify \
  -H "Authorization: Bearer em_abc123..."

{"status": "ok", "message": "SMTP connection verified"}

After configuring SMTP, all subsequent emails sent with that API key will use your server instead of the Ethereal sandbox. Works with Gmail, Outlook, Amazon SES, Postmark, or any standard SMTP provider.

Sending Emails with Attachments

curl -X POST https://agent-gateway-kappa.vercel.app/v1/agent-email/api/send \
  -H "Authorization: Bearer em_abc123..." \
  -H "Content-Type: application/json" \
  -d '{
    "to": "team@example.com",
    "subject": "Monthly Report - March 2026",
    "text": "Please find the monthly report attached.",
    "attachments": [
      {
        "filename": "report.pdf",
        "content": "JVBERi0xLjQK...",
        "encoding": "base64",
        "contentType": "application/pdf"
      }
    ],
    "cc": ["manager@example.com"],
    "replyTo": "noreply@example.com"
  }'

Delivery Logs

Track every email you've sent with the logs endpoint:

curl https://agent-gateway-kappa.vercel.app/v1/agent-email/api/logs?limit=5 \
  -H "Authorization: Bearer em_abc123..."

{
  "total": 12,
  "emails": [
    {
      "id": "a1b2c3d4-...",
      "to": ["user@example.com"],
      "subject": "Order Confirmation #1234",
      "status": "sent",
      "messageId": "<abc@mail.ethereal.email>",
      "timestamp": "2026-03-03T15:42:18.123Z",
      "duration_ms": 342
    }
  ]
}

Real-World Use Cases

Comparison: Free Email API vs Alternatives

Key advantage: Agent Email gets you sending emails in under 30 seconds — no account creation, no domain verification, no credit card. For production, bring your own SMTP and you get the full power of Gmail, SES, or any provider through a simple REST wrapper.

FAQ