Email Verifier

Verify whether email addresses are deliverable by connecting to the recipient's mail server and checking if it accepts the address — without actually sending any mail.

How It Works

1. MX Lookup — Resolves the domain's mail exchange server
2. SMTP Handshake — Connects to the MX server on port 25
3. RCPT TO Check — Asks the server if it would accept mail for the address
4. Catch-All Detection — Tests a random address to detect catch-all domains

Dependencies

pip3 install dnspython

Usage

Single or multiple emails

python3 scripts/verify_email.py [email protected] [email protected]

From stdin

echo "[email protected]" | python3 scripts/verify_email.py --stdin

From CSV (e.g., a lead list)

python3 scripts/verify_email.py --csv leads.csv --email-column "Contact Email"

Options

• --helo DOMAIN — HELO domain for SMTP greeting (default: verify.local)
• --timeout SECONDS — Connection timeout (default: 10)

Output

JSON array to stdout. Each result contains:

{
  "email": "[email protected]",
  "domain": "example.com",
  "mx_host": "aspmx.l.google.com",
  "smtp_code": 250,
  "smtp_response": "2.1.5 OK",
  "deliverable": "yes"
}

Deliverability values

Rate Limiting

The script includes built-in rate limiting to protect your IP reputation:

# Defaults: 1s between checks, max 20 per domain before 30s pause
python3 scripts/verify_email.py --csv leads.csv --email-column "Contact Email"

# Conservative: slower checks, lower burst limit
python3 scripts/verify_email.py --delay 3 --max-per-domain 10 --burst-pause 60 [email protected]

# Aggressive (not recommended from residential IPs)
python3 scripts/verify_email.py --delay 0.5 --max-per-domain 50 [email protected]

Options

• --delay SECONDS — Pause between each check (default: 1.0)
• --max-per-domain N — Max checks to one domain before pausing (default: 20)
• --burst-pause SECONDS — How long to pause after hitting the per-domain limit (default: 30)

Why rate limiting matters