Useful Python script to know if an email address exists, based on Inti's Medium post https://medium.com/intigriti/abusing-autoresponders-and-email-bounces-9b1995eb53c2

does_email_address_exist.py

#!/usr/bin/python3
# Example usage: ./does_email_address_exist.py twitter.com jack
import argparse
from smtplib import SMTP
import dns.resolver

parser = argparse.ArgumentParser() 
parser.add_argument('hostname')
parser.add_argument('user')
args = parser.parse_args()

hostname = args.hostname
user = args.user

mx_records = dns.resolver.query(hostname, 'MX')
server = str(mx_records[0].exchange)

with SMTP(server, local_hostname=hostname) as smtp:
  smtp.helo()
  smtp.docmd('mail from: <[email protected]>')
  code, text = smtp.docmd('rcpt to: <'+user+'@'+hostname+'>')
  if code == 550:
    print('it does not')
  else:
    print('it does exist')