Integrate email verification
in under 10 minutes

Base URL

All requests are over HTTPS. Insecure HTTP calls are rejected with a 400 code.

Authentication

All requests require a Bearer token in the Authorization header. Your API key is available in the dashboard, under Settings > API Key.

Authorization: Bearer mc_live_xxxxxxxxxxxxxxxxxxxx

POST /v1/verify, verifying an address

Verifies a single email address. Returns the status, the score and the verification details.

Request

{
  "email": "[email protected]",
  "options": {
    "catch_all": true
  }
}

Response format

The response is a JSON object with the following fields:

{
  "email":      "[email protected]",
  "status":     "valid",
  "score":      97,
  "checks": {
    "syntax":     true,
    "dns":        true,
    "mx":         true,
    "smtp":       true,
    "disposable": false,
    "catch_all":  false
  },
  "confidence": "high"
}

Returned statuses

cURL example

# Verify an email address
curl -X POST https://api.mailcheck.fr/v1/verify \
  -H "Authorization: Bearer mc_live_xxxxxxxxxxxxxxxxxxxx" \
  -H "Content-Type: application/json" \
  -d '{"email":"[email protected]","options":{"catch_all":true}}'

Python example

import os
import requests

API_KEY = os.environ["MAILCHECK_API_KEY"]

def verify_email(email: str) -> dict:
    response = requests.post(
        "https://api.mailcheck.fr/v1/verify",
        headers={
            "Authorization": f"Bearer {API_KEY}",
            "Content-Type": "application/json"
        },
        json={
            "email": email,
            "options": {"catch_all": True}
        },
        timeout=5
    )
    response.raise_for_status()
    return response.json()

# Usage example
result = verify_email("[email protected]")
if result["status"] == "valid":
    print(f"✓ Valid email · Score: {result['score']}")
else:
    print(f"✗ Status: {result['status']}")

Node.js example

const API_KEY = process.env.MAILCHECK_API_KEY;

async function verifyEmail(email) {
  const res = await fetch("https://api.mailcheck.fr/v1/verify", {
    method: "POST",
    headers: {
      "Authorization": `Bearer ${API_KEY}`,
      "Content-Type": "application/json"
    },
    body: JSON.stringify({
      email,
      options: { catch_all: true }
    })
  });

  if (!res.ok) {
    throw new Error(`API error: ${res.status}`);
  }

  return res.json();
}

// Usage example
verifyEmail("[email protected]")
  .then(data => {
    console.log(`Status: ${data.status} · Score: ${data.score}`);
  })
  .catch(console.error);

Rate limits

Limits apply per API key over a sliding window of 1 second.

When exceeded, the API returns a 429 Too Many Requests with a Retry-After header indicating the wait time in seconds.

MCP connector, plug your data into Claude

The MCP connector gives Claude read access to your open tracking data. You ask in plain language, Claude queries mailcheck and answers. No key to paste into a configuration file, authorisation goes through OAuth.

Available on accounts with an active subscription, any plan, including the Tracking plan at 9 EUR per month.

Setup, three steps

In Claude, open settings then Connectors, click Add connector and paste the URL above. You are redirected to mailcheck to authorise access, then sent back to Claude.

The five tools

Questions you can ask

• Who has not opened my emails this week?
• How many times did this client open my proposal?
• What is my average time between sending and the first open?
• Which recipients came back to a message more than once?

What the connector does not do

Access is read only. The connector cannot send an email, change your data, or read the body of your messages. It exposes the subject, recipient, sender and open timestamps, nothing else. Every tool is scoped to your own account.

Open tracking via API, for a custom SMTP server

The Chrome extension covers Gmail and Zoho Mail automatically. If you send from your own SMTP server, you get the same open tracking with two calls: one to register the email, one invisible pixel in the message body. Opens then show up in your dashboard and in the MCP connector, exactly like any email tracked by the extension.

A different base from the verification API above. Same API key, same Authorization: Bearer header.

1. Register the email before sending

curl -X POST https://wk.mailcheck.fr/tracking/emails \
  -H "Authorization: Bearer sk-mc-xxxxxxxxxxxxxxxxxxxx" \
  -H "Content-Type: application/json" \
  -d '{"id":"3fa85f64-5717-4562-b3fc-2c963f66afa6","subject":"Your quote","recipient":"[email protected]","sender":"[email protected]","provider":"smtp"}'

2. Add the pixel to the HTML body

Insert this image, with the same id, before sending through your SMTP server:

<img src="https://wk.mailcheck.fr/o/3fa85f64-5717-4562-b3fc-2c963f66afa6.gif" width="1" height="1" alt="">

This route needs no authentication, like any tracking pixel: it records the open and returns a transparent 1x1 GIF.

Free plan limits

10 tracked emails per calendar month, one provider at a time (the provider value of the first email of the month locks the rest). Unlimited tracking across every provider from the Tracking plan at 9 EUR/month.

What the self-open filter does not cover here

The extension ignores your own rereads by comparing the IP address at send time to the one at open time. With an SMTP server, the email is registered from your server, so that fingerprint is your server's, not your browser's. The filter stays harmless, it simply does not apply to this particular case.

Error codes

{
  "error": "insufficient_credits",
  "message": "Your monthly quota is exhausted. Upgrade your plan.",
  "credits_remaining": 0
}