Use dnspython library to validate an email domain via DNS MX, AAAA, and A records. A sanity check that avoids abusing the email server.

dns_check_email_domain.py

import re
import dns.resolver

def dns_check_email_domain(domain):
    """
    Query DNS records to verify that email server is possible on domain.

    If no DNS records are found, user should confirm email address.
    """
    response = {}
    # Check for '.' in domain to filter out relative domains
    if re.match('^.+\..+$', domain, re.I) is None:
        msg = "Not possibly a valid domain: '{}'".format(domain)
        response['error'] = msg
        return response
    record_types = ('MX', 'AAAA', 'A')
    for record_type in record_types:
        try:
            if len(dns.resolver.query(domain, record_type)):
                msg = "Found {} record(s) for {}".format(record_type, domain)
                response['success'] = msg
                return response
        except:
            continue
    msg = "No DNS records of types {} found for {}".format(record_types, domain)
    response['warning'] = msg
    return response