VRFY SMTP async

smtp.py

import smtplib
import time
import concurrent.futures

smtp_server = "10.129.217.194" 
port = 25

def get_email(email):
    with smtplib.SMTP(smtp_server, port) as server:
        print('trying to get', email)
        code, response = server.docmd("VRFY", email)
        if code == 252:
            return email

with open("lista.txt", "r") as f:
    emails = f.read().splitlines()

with concurrent.futures.ThreadPoolExecutor() as executor:
    futures = []
    for index, email in enumerate(emails):
        futures.append(executor.submit(get_email, email))
    for future in concurrent.futures.as_completed(futures):
        result = future.result()
        if result:
            print('===========')
            print(result)