Updated January 29, 2026

TL;DR: The Hunter.io API automates B2B email discovery through Domain Search and Email Finder endpoints, but credits add up fast. For 10,000 leads, expect $199/month on Hunter's Business plan plus script maintenance overhead. If you run an agency and need verified emails flowing into campaigns, Instantly SuperSearch offers flat-fee pricing with 450M+ contacts, built-in verification, and unlimited sending accounts. This guide covers Hunter API implementation and explains why agencies switch to integrated platforms.

Running manual email searches works for 10 leads. For 10,000, you need an API or a better platform. This guide walks through the technical details of implementing the Hunter.io API for automated email discovery and shows you the math on why agency operators often switch to integrated platforms.

What is the Hunter Find Email API?

The Hunter.io API provides programmatic access to B2B contact data. You use two primary endpoints for email discovery:

• Domain Search: Returns all email addresses found for a given company domain, along with confidence scores and sources
• Email Finder: Finds the most likely email address for a specific person when you provide their name and company domain

Both endpoints return JSON responses with confidence scores indicating the probability that the email address is correct. The confidence calculation depends on the number and quality of public sources where the address appears.

Key terminology distinctions:

The API base URL for all requests is https://api.hunter.io/v2/. You authenticate by passing your API key as a query parameter, in the X-API-KEY header, or using Bearer token authorization.

How to use the Hunter.io API for email finding

Setting up the Hunter.io API requires four steps: authentication, structuring requests, parsing responses, and verifying deliverability.

Step 1: Get your API key

After creating a Hunter.io account, navigate to your dashboard to find your API key. The free plan includes 25 email searches and 50 verification credits per month for testing. You can use a test API key (test-api-key) during development, which validates parameters but returns dummy data.

Step 2: Domain Search request

The Domain Search endpoint finds all emails associated with a company. Here is a Python example:

import requests

api_key = "your_api_key_here"
domain = "stripe.com"

url = f"https://api.hunter.io/v2/domain-search?domain=%7Bdomain%7D&api_key=%7Bapi_key%7D"

response = requests.get(url)
data = response.json()

for email in data["data"]["emails"]:
    print(f"{email['value']} - Confidence: {email['confidence']}%")

The equivalent cURL command:

curl "https://api.hunter.io/v2/domain-search?domain=stripe.com&api_key=your_api_key_here"

Step 3: Email Finder request

When you know the person's name, the Email Finder returns their specific address:

import requests

api_key = "your_api_key_here"
domain = "stripe.com"
first_name = "Patrick"
last_name = "Collison"

url = f"https://api.hunter.io/v2/email-finder?domain=%7Bdomain%7D&first_name=%7Bfirst_name%7D&last_name=%7Blast_name%7D&api_key=%7Bapi_key%7D"

response = requests.get(url)
data = response.json()

print(f"Email: {data['data']['email']}")
print(f"Confidence: {data['data']['score']}%")
print(f"Verification Status: {data['data']['verification']['status']}")

The Email Finder costs 1 credit per call. You must provide either a domain name or company name, plus the person's first and last name. Alternatively, you can provide just a LinkedIn handle without name information. In production, always check for null responses since the Email Finder returns no result when it cannot match the pattern with sufficient confidence.

Step 4: Check deliverability status

Check the verification object in the response for a status field. Valid statuses include:

• valid: The email exists and accepts mail
• invalid: The address does not exist
• accept_all: The server accepts all addresses (cannot verify individual existence)
• webmail: Personal webmail address detected
• disposable: Temporary email address

Always filter for "valid" status before adding contacts to campaigns. Sending to unverified addresses damages sender reputation, which matters more than volume for agencies managing multiple client domains.

Building an automated enrichment pipeline

Production integrations need to handle rate limits, errors, and CRM field mapping. Here is what to plan for.

Rate limits and throttling

Hunter limits the Email Finder endpoint to 15 requests per second and 500 requests per minute. The Email Verifier has stricter limits at 10 requests per second and 300 requests per minute.

When you hit these limits, the API returns a 403 error. Implement exponential backoff to handle this:

import time
import requests

def make_request_with_retry(url, max_retries=5):
    delay = 1
    for attempt in range(max_retries):
        response = requests.get(url)
        if response.status_code == 403:
            time.sleep(delay)
            delay *= 2  # Exponential backoff: 1s, 2s, 4s, 8s, 16s
        else:
            return response
    return None

Error handling for common scenarios

You will encounter these standard HTTP error codes:

1. 401 Authentication Failed

{
  "errors": [{
    "id": "authentication_failed",
    "code": 401,
    "details": "No user found for the API key supplied"
  }]
}

1. 400 Missing Parameters

{
  "errors": [{
    "id": "wrong_params",
    "code": 400,
    "details": "You are missing the domain parameter"
  }]
}

1. 202 Pending Verification (Greylisting)

Some mail servers temporarily delay verification requests as spam prevention. The API returns 202, meaning retry the request after 1-12 hours.

CRM field mapping

Map the JSON response fields to your CRM schema. Salesforce and HubSpot: Hunter fields align with common CRM objects in predictable ways. Custom fields: You may need to create custom properties for confidence scores and LinkedIn URLs. Here is how Hunter fields align with common CRM objects:

For Salesforce and HubSpot integrations, you can use OutboundSync to handle bidirectional sync or build custom Zapier flows. Instantly's HubSpot integration handles synchronization between outreach efforts and your CRM without maintaining custom code.

The cost of scaling: Hunter API vs. Instantly SuperSearch

Here is where the math matters for agencies.

Pricing comparison

Hunter's Business plan costs $199/month and includes 10,000 email searches plus 20,000 verification credits. That sounds reasonable until you factor in the success rate. Hunter's Email Finder does not always return a result, so your actual cost per verified email runs higher than the plan's nominal rate.

Instantly SuperSearch uses a waterfall enrichment model with 5+ data providers, averaging about 1.5 credits per verified work email. The Hyper Credits plan provides 10,000 credits at $197/month.

The hidden cost: tool sprawl

The bigger issue is workflow friction. With Hunter's API, you:

1. Write and maintain custom scripts
2. Handle rate limits and retries
3. Export data to CSV
4. Import into your sending tool
5. Deal with format mismatches and deduplication

With Instantly, verified leads flow directly into campaigns with a few clicks. As one agency operator shared:

"I like that instantly can handle large scale email campaigns without worrying about deliverability. The automation for inbox rotation, warm up and sending limits makes outreach very smooth and saves a lot of manual work." - Anjali T on G2

The time spent maintaining enrichment scripts is time not spent on campaign strategy. For agencies billing clients on results, that trade-off matters.

Watch this full Instantly tutorial to see the complete workflow from lead search to campaign launch.

How to automate email finding and sending with Instantly

Instantly SuperSearch combines lead discovery, verification, and campaign management in one interface.

Step 1: Filter by ideal customer profile

Navigate to SuperSearch and use filters or AI Search to define your target audience:

• AI Search: Type a natural language query like "Founders of SaaS companies in New York with 50-100 employees"
• Manual Filters: Select job title, industry, location, revenue range, tech stack, and keywords

The database includes 450M+ B2B contacts with LLM-assisted enrichment that catches emails pattern-based tools miss, especially at companies with non-standard email formats.

Step 2: Enrich and verify contacts

Click "Find Email" on your search results. SuperSearch runs waterfall enrichment across multiple providers, returning only verified work emails. You pay credits only for successful matches, not for search attempts.

Step 3: Push directly to campaigns

Select leads and click "Add to Campaign." Instantly checks for duplicates across all your campaigns automatically. The platform supports unlimited email accounts on all plans, so you can distribute sends across dozens of inboxes without per-seat fees.

"Setting up campaigns is quick and straightforward, which allows us to run multiple campaigns simultaneously. The platform enables us to target various job titles efficiently, making our outbound acquisition efforts more effective." - Ben G on G2

Step 4: Monitor and optimize

Use detailed reporting to track open rates, replies, and bounce rates. The analytics integrate easily with BI dashboards for client reporting.

For agencies managing multiple clients, built-in warmup keeps sender reputation healthy across all accounts. The platform's 4.2M+ account deliverability network handles inbox warm-up automatically.

"The automated warm-up, unlimited email sending, and smart campaign management saved me hours every week." - Saleph on Trustpilot

Remember to cap at 30 sends per inbox per day and warm new accounts for 30 days before scaling volume. This approach protects client domains while you ramp throughput.

For a video walkthrough of cold email setup, check how within 10 minutes you can set up your first campaign.

Setting up multi-factor authentication

Microsoft 365 requires multi-factor authentication for email access. During first login, you will configure a second verification method (phone, authenticator app, or security key). Note that Microsoft 365 MFA is separate from CUNY MFA used for applications like CUNYfirst and Brightspace.

Students can keep their Hunter email address after graduation, which makes it useful as a long-term professional contact.

Scale your outreach without the API overhead

Building custom enrichment pipelines gives you control over data flow, but for most agencies, the math favors integrated platforms. Instantly combines verified data, unlimited sending accounts, and deliverability tools in one subscription. You filter leads, click "Add to Campaign," and focus on copy that converts.

"I built my entire client acquisition system through instantly.ai & also sell the product as a service to my clients which is my entire business model." - Joshua Blacklidge on Trustpilot

For teams using N8N for automation, this cold email outreach workflow shows how to connect lead generation with Instantly campaigns.

Ready to skip the API complexity? Try Instantly free and run SuperSearch on your next campaign.

Frequently asked questions about Hunter email

Is email scraping with Hunter legal?
Hunter.io collects publicly available business emails and is GDPR compliant. Legality depends on your use case and compliance with CAN-SPAM and local regulations.

Can I use Hunter.io for free?
Yes. The free plan includes 25 email searches and 50 verification credits per month for testing.

What are Hunter.io API rate limits?
Domain Search and Email Finder allow 15 requests per second. Email Verifier is stricter at 10 requests per second and 300 per minute.

Key terms glossary

API Endpoint: A specific URL path where your code sends requests to retrieve or submit data.

JSON: JavaScript Object Notation, a lightweight data format used for API responses and requests.

NetID: A unique identifier assigned to CUNY students and staff for system authentication.

Deliverability: The percentage of sent emails that land in the primary inbox rather than spam or bounce. Keep bounce rates at or below 1 percent.

SuperSearch: Instantly's lead database feature providing access to 450M+ B2B contacts with waterfall enrichment.

Waterfall Enrichment: A method that queries multiple data providers in sequence to maximize email match rates.