Test if an email exists by trying to send an email (but not doing it)

test_email.py

#!/bin/env python

# Test email address
# return code :
#   0 -> OK
#   1 -> Not Valid
#   2 -> Could not connect to mail server

from sys import argv, exit
import dns.resolver
import smtplib

if __name__ == '__main__':
        email = argv[1]
        user, domain = email.split("@")
        
        try:
                ans = dns.resolver.query(domain, "MX")
        except dns.resolver.NoAnswer:
                print("Domain doesn't have MX records")
                exit(1)
        except dns.resolver.NXDOMAIN:
                print("Domain doesn't exist")
                exit(1)
                
        # Sort email servers by preferences
        sorted_mail_servers = sorted(ans, key=lambda x: x.preference)
        
        for mail_server in sorted_mail_servers:
                server_name = mail_server.exchange.to_text()[:-1]  # remove last dot
                try:
                        print("Try to connect to {}".format(server_name))
                        m = smtplib.SMTP(server_name, 25)
                except:
                        print("Error at connecting server {}".format(server_name))
                        continue
                        
                print("Connected")
                
                status, resp = m.ehlo("example.org")
                if status != 250:
                        print("EHLO refused: {}".format(resp))
                        exit(1)
                print("Sent EHLO")
                
                if "STARTTLS" in resp:
                        m.starttls()
                        print("Initiated STARTTLS")
                        m.ehlo("example.org")
                        
                status, resp = m.mail("[email protected]")
                if status != 250:
                        print("Error at MAIL FROM: {}".format(resp))
                        exit(1)
                print("Sent MAIL FROM")
                
                status, resp = m.rcpt(email)
                if status != 250:
                        print("Error at RCPT TO: {}".format(resp))
                        exit(1)
                print("Sent RCPT TO")
                
                exit(0)
                
        print("Could not connect to a server")
        exit(2)