Email Validation API — Real-Time Verification for Developers

Quick start

One curl call away from your first verification:

curl -X POST "https://api.getkillbounce.com/api/v1/verify/single" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"email":"john@example.com"}'

Response:

{
  "email": "john@example.com",
  "status": "valid",
  "is_valid": true,
  "reason": "Email is deliverable",
  "score": 98,
  "syntax_valid": true,
  "domain_exists": true,
  "smtp_valid": true,
  "is_disposable": false,
  "is_role_based": false,
  "is_catch_all": false,
  "mx_records": ["aspmx.l.google.com"],
  "smtp_provider": "Google Workspace"
}

Response fields explained

Integration examples

1. 01

   JavaScript / Node.js

   Validate on form submit — block the submission if status is anything other than valid.

const verifyEmail = async (email) => {
  const r = await fetch('https://api.getkillbounce.com/api/v1/verify/single', {
    method: 'POST',
    headers: {
      'Authorization': `Bearer ${process.env.KILLBOUNCE_API_KEY}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({ email }),
  })
  return r.json()
}

// On form submit
const result = await verifyEmail('user@example.com')
if (result.status !== 'valid') {
  showError('Please enter a valid email address.')
}

1. 01

   Python

   Same flow, requests library:

import requests

def verify_email(email: str) -> dict:
    r = requests.post(
        "https://api.getkillbounce.com/api/v1/verify/single",
        json={"email": email},
        headers={"Authorization": f"Bearer {API_KEY}"},
        timeout=10,
    )
    return r.json()

result = verify_email("user@example.com")
if result["status"] == "valid":
    print("Safe to proceed")

1. 01

   PHP

   Minimal cURL wrapper for legacy stacks:

function verifyEmail($email) {
    $ch = curl_init('https://api.getkillbounce.com/api/v1/verify/single');
    curl_setopt_array($ch, [
        CURLOPT_POST => true,
        CURLOPT_POSTFIELDS => json_encode(['email' => $email]),
        CURLOPT_HTTPHEADER => [
            'Authorization: Bearer ' . API_KEY,
            'Content-Type: application/json',
        ],
        CURLOPT_RETURNTRANSFER => true,
    ]);
    return json_decode(curl_exec($ch), true);
}

Use cases

1. 01

   Signup form validation

   Block disposable and invalid emails at registration. Reduce fake accounts and improve user quality from day one.

2. 02

   Lead capture forms

   Validate emails on landing pages before leads enter your CRM. Keep your Salesforce or HubSpot database clean automatically.

3. 03

   E-commerce checkout

   Verify customer email at checkout to ensure order confirmations, shipping updates, and receipts actually reach them.

4. 04

   Newsletter subscribe

   Prevent bad emails from inflating your subscriber count and damaging your ESP sender score.

Rate limits & quotas

API rate limits are designed to be generous for production traffic and tight enough to prevent runaway loops or abuse. Authenticated requests scale with your account's credit balance:

Exceeded limits return HTTP 429 with a standard Retry-After header. The header tells you how many seconds to wait before retrying — use it for exponential backoff rather than blind retries.

Error handling

Every error response follows the same shape so your error handler stays simple. Status codes map to real failure modes — none of this 'everything is 200 with status:error inside the body' nonsense:

{
  "error": {
    "code": 402,
    "message": "Insufficient credits. You have 0 credits remaining.",
    "type": "PaymentRequiredException",
    "path": "/api/v1/verify/single"
  }
}

Webhook callbacks for bulk jobs

Bulk verification jobs run asynchronously — they can take minutes to hours depending on list size. Instead of polling, register a webhook URL and KillBounce will POST to it the moment a job completes:

// You POST this to /verify/bulk
{
  "file_url": "https://your-cdn.com/list.csv",
  "webhook_url": "https://yourapp.com/webhooks/killbounce"
}

// We POST this to your webhook when it's done
{
  "event": "job.completed",
  "job_id": "job_a1b2c3d4",
  "status": "completed",
  "total_emails": 50000,
  "valid": 42150,
  "invalid": 5230,
  "catch_all": 1620,
  "disposable": 480,
  "unknown": 520,
  "download_url": "https://api.getkillbounce.com/jobs/job_a1b2c3d4/download"
}

Webhook payloads are signed with HMAC-SHA256 (Svix-compatible) — verify the signature before trusting the data. The download URL is signed and expires in 24 hours.

Authentication & security

• Bearer token authentication via Authorization header
• X-API-Key header accepted as an alternative
• Keys generated, rotated, and revoked from the dashboard
• All traffic encrypted over HTTPS / TLS 1.2+
• SOC 2-compliant infrastructure (Tier IV datacenter)
• Email payloads never logged or retained beyond response time
• Webhooks signed with HMAC-SHA256 for verification