Email Validator API

A REST API that validates email addresses through 3 layers: syntax - MX record - deliverability verification. Returns a 0-100 score and actionable recommendation.

Built for GTM teams who need to clean lead lists before loading into a CRM or sending outbound sequences.

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What It Does

Input: john@stripe.com
         ↓
  [Layer 1] Syntax check      — valid format?
         ↓
  [Layer 2] MX record check   — does the domain accept email?
         ↓
  [Layer 3] API verification  — is this mailbox real? (Hunter.io / ZeroBounce)
         ↓
Output: score (0–100), deliverability, recommendation

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Stack

Layer	Tool
API framework	Flask 3.0
DNS checks	dnspython
Deliverability	Hunter.io API (free tier)
Secondary check	ZeroBounce (optional)

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Quickstart

# 1. Clone
git clone https://github.com/stevenkaranja/email-validator-api
cd email-validator-api

# 2. Install
pip install -r requirements.txt

# 3. Configure
cp .env.example .env
# Add your Hunter.io API key (optional — works without it)

# 4. Start the server
python app.py

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Endpoints

GET /validate?email=<email>

Validate a single email.

curl "http://localhost:5000/validate?email=john@stripe.com"

Response:

{
  "email": "john@stripe.com",
  "domain": "stripe.com",
  "score": 87,
  "deliverability": "High",
  "syntax_valid": true,
  "mx_valid": true,
  "is_disposable": false,
  "is_role_based": false,
  "api_status": "valid",
  "mx_host": "aspmx.l.google.com",
  "recommendation": "Send — high deliverability"
}

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POST /validate/batch

Validate up to 50 emails at once.

curl -X POST http://localhost:5000/validate/batch \
  -H "Content-Type: application/json" \
  -d '{"emails": ["john@stripe.com", "fake@mailinator.com", "info@hubspot.com"]}'

Response:

{
  "summary": {
    "total": 3,
    "high_deliverability": 1,
    "medium_deliverability": 1,
    "low_deliverability": 1,
    "disposable": 1
  },
  "results": [...]
}

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GET /health

curl http://localhost:5000/health
# {"status": "ok", "service": "email-validator-api"}

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Scoring Logic

Check	Points
Valid syntax	20
MX record found	25
API status: valid	40
API status: accept_all	25
Not disposable	10
Not role-based	5

Score	Deliverability
80–100	High — Send
50–79	Medium — Send with caution
0–49	Low — Skip

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Author

Stephen Karanja — AI Automation & GTM Systems Engineer
stephenkaranja.vercel.app · LinkedIn