Checks whether or not an email actually exists

check_email.py

#!/usr/bin/env python
# Requires dnspython

from __future__ import print_function
from dns.exception import DNSException
from dns.resolver import query
from smtplib import SMTP, SMTPException

def get_mx_records(domain):
    try:
        records = query(domain, 'MX')
    except DNSException:
        records = []
    return (r.exchange.to_text(omit_final_dot=True) for r in records)

def check_email_address(hostname, email):
    smtp = SMTP(hostname)
    code, msg = smtp.helo('localhost')
    code, msg = smtp.mail('<testing@testing.com>')
    code, msg = smtp.rcpt('<%s>' % email)
    return code in (250, 251)

def is_valid_email(email):
    domain = email.partition('@')[2]
    for hostname in get_mx_records(domain):
        try:
            is_valid = check_email_address(hostname, email)
        except SMTPException:
            continue
        else:
            break
    else:
        is_valid = False
    return is_valid

if __name__ == '__main__':
    import sys 
    
    for arg in sys.argv[1:]:
        print("{} is".format(arg), end='')
        if is_valid_email(arg):
            print("valid")
        else:
            print("invalid")