Email Validator

from dns import resolver
import smtplib
import socket
import re
# http://www.pillalamarri.in/python/email-validator/
# FIRST CHECK


def check_syntax(email):
    regex = r'^[a-z0-9]+[\._]?[a-z0-9]+[@]\w+[.]\w{2,3}$'
    if(re.search(regex, email)):
        print("Check 1 (Syntax) Passed")
    else:
        print("Check 1 FAILED! Bad Syntax, Invalid Email!")
        exit()

# SECOND CHECK


def check_dns(email, domain):
    try:
        records = resolver.resolve(domain, 'MX')
        mxRecord = str(records[0].exchange)
        print("Check 2 (DNS -", mxRecord+") Passed")
        return mxRecord
    except:
        print("Check 2 FAILED! The domain", domain,
              "does not exist, Invalid Email!")
        exit()

# THIRD CHECK


def check_response(email, domain, mxRecord):
    try:
        # Get local server hostname
        host = socket.gethostname()

        # SMTP lib setup (use debug level for full output)
        server = smtplib.SMTP()
        server.set_debuglevel(0)

        # SMTP Conversation
        server.connect(mxRecord)
        server.helo(host)
        server.mail(email)
        code, message = server.rcpt(str(email))
        server.quit()

        # Assume 250 as Success
        if code == 250:
            print("Check 3 (SMTP response) Passed")
            print(email, "is a VALID email address!")
        else:
            print("Check 3 FAILED! The user", email.split(
                "@")[0], "does not exist, Invalid Email!")
    except socket.error as socketerror:
        print("Check 3 HALTED! The domain", domain,
              ", either does not have an SMTP or have restricted access through external scripts")


email = input("Enter your Email id :")
domain = email.split("@")[-1]
check_syntax(email)  # CHECK1
mxRecord = check_dns(email, domain)  # CHECK2
check_response(email, domain, mxRecord)  # CHECK3
# http://www.pillalamarri.in/python/email-validator/