Here is snipet code to run python .
It does read from a file with domain names , one per row.
It does produce emails in an output file, one email per row.

import json

import requests

from concurrent.futures import ThreadPoolExecutor

# File paths

input_file_path = 'domains.txt'  # Replace 'file_A.csv' with your input file path

output_file_path = 'emails_output.txt'  # Replace 'file_B.csv' with your output file path

key =''


# Function to process a single row

def process_row(row):

    api_url = 'https://api.minelead.io/v1/search/?domain='+row+'&key='+key+'&max-emails=3'

    response = requests.get(api_url)

    data = response.content

    try:

        data = json.loads(data.strip())

        return data

    except json.JSONDecodeError:

        print(f"Error decoding JSON in row: {row}")

        return None


# Function to extract emails from data and write them to output file

def extract_and_write_emails(data, output_file):

    if 'emails' in data:

        emails = [email['email'] for email in data['emails']]

        domain = data['domain']

        with open('emails_output.txt', 'a') as file:

            for email in emails:

                file.write(f"{domain}, {email}\n")


# Open input and output files

with open(input_file_path, 'r') as input_file, open(output_file_path, 'a') as output_file:

    # Create a thread pool executor

    with ThreadPoolExecutor(max_workers=3) as executor:

        # Process each row in a separate thread

        futures = [executor.submit(process_row, row) for row in input_file]


        # Process the results

        for future in futures:

            data = future.result()

            if data:

                extract_and_write_emails(data, output_file)