Email validation

import asyncio

import aiodns
from aiosmtplib import SMTP, SMTPException, SMTPStatus
from async_timeout import timeout

async def _validate_email(email, loop):
    domain = email.split('@', 1)[1]
    resolver = aiodns.DNSResolver(loop=loop)
    with timeout(2, loop=loop):
        v = await resolver.query(domain, 'MX')

        host = v[0][0]
        smtp = SMTP(hostname=host, port=25, loop=loop)
        code, ans1 = await smtp.connect()
        if code != SMTPStatus.ready:
            raise EmailError(f'wrong smtp response {code} (expected 220) ans="{ans1}"')
        code, ans2 = await smtp.helo()
        if code != SMTPStatus.completed:
            raise EmailError(f'wrong smtp response {code} (expected 250) ans="{ans2}"')
        # could also do the following but probably too far
        code, ans3 = await smtp.mail('whatever@example.com')
        debug(code, ans3)
        code, ans4 = await smtp.rcpt(email)
        debug(code, ans4)
    logger.info('"%s": host=%s, connect ans="%s", helo ans="%s"', email, host, ans1, ans2)