Restructure SMTP check code
This commit is contained in:
Reinhard Müller
parent
59172783ce
commit
ef15fa994a
1 changed files with 168 additions and 112 deletions
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@ -1,8 +1,7 @@
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from logging import getLogger
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from smtplib import SMTP, SMTPNotSupportedError, SMTPServerDisconnected
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from socket import error as SocketError
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from socket import gethostname
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from typing import Optional, Tuple
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from smtplib import (
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SMTP, SMTPNotSupportedError, SMTPResponseException, SMTPServerDisconnected)
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from typing import List, Optional
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from dns.exception import Timeout
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from dns.rdatatype import MX as rdtype_mx
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@ -20,21 +19,6 @@ from .exceptions import (
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LOGGER = getLogger(name=__name__)
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class _ProtocolError(Exception):
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"""
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Raised when there is an error during the SMTP conversation.
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Used only internally.
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"""
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def __init__(self, command: str, code: int, message: bytes):
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self.command = command
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self.code = code
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self.message = message.decode(errors='ignore')
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def __str__(self):
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return f'{self.code} {self.message} (in reply to {self.command})'
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def _get_mx_records(domain: str, timeout: int) -> list:
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'Return the DNS response for checking, optionally raise exceptions.'
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try:
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@ -73,18 +57,74 @@ def _get_cleaned_mx_records(domain: str, timeout: int) -> list:
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return result
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def _smtp_ehlo_tls(smtp: SMTP, helo_host: str):
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class _SMTPChecker(SMTP):
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"""
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Try and start the TLS session, fall back to unencrypted when
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unavailable.
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A specialized variant of `smtplib.SMTP` for checking the validity of
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email addresses.
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All the commands used in the check process are modified to raise
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appropriate exceptions: `SMTPServerDisconnected` on connection
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issues and `SMTPResponseException` on negative SMTP server
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responses. Note that the methods of `smtplib.SMTP` already raise
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these exceptions on some conditions.
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Also, a new method `check` is added to run the check for a given
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list of SMTP servers.
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"""
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code, message = smtp.ehlo(name=helo_host)
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if code >= 400:
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# EHLO bails out, no further SMTP commands are acceptable
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raise _ProtocolError('EHLO', code, message)
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def __init__(
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self, local_hostname: str, timeout: float, debug: bool,
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raise_communication_errors: bool,
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raise_temporary_errors: bool,
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sender: str, recip: str):
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"""
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Initialize the object with all the parameters which remain
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constant during the check of one email address on all the SMTP
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servers.
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"""
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super().__init__(local_hostname=local_hostname, timeout=timeout)
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self.set_debuglevel(debuglevel=2 if debug else False)
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self.__raise_communication_errors = raise_communication_errors
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self.__raise_temporary_errors = raise_temporary_errors
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self.__sender = sender
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self.__recip = recip
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self.__communication_errors = {}
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self.__temporary_errors = {}
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# Avoid error on close() after unsuccessful connect
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self.sock = None
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def putcmd(self, cmd, args=""):
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"""
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Like `smtplib.SMTP.putcmd`, but remember the command for later
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use in error messages.
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"""
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if args:
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self.__command = f'{cmd} {args}'
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else:
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self.__command = cmd
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super().putcmd(cmd, args)
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def connect(self, host, *args, **kwargs):
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"""
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Like `smtplib.SMTP.connect`, but raise appropriate exceptions on
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connection failure or negative SMTP server response.
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"""
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self.__command = 'connect' # Used for error messages.
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self._host = host # Missing in standard smtplib!
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try:
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smtp.starttls()
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code, message = smtp.ehlo(name=helo_host)
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code, message = super().connect(host, *args, **kwargs)
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except OSError as error:
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raise SMTPServerDisconnected(str(error))
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if code >= 400:
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raise SMTPResponseException(code, message)
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return code, message
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def starttls(self, *args, **kwargs):
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"""
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Like `smtplib.SMTP.starttls`, but continue without TLS in case
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either end of the connection does not support it.
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"""
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try:
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super().starttls(*args, **kwargs)
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except SMTPNotSupportedError:
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# The server does not support the STARTTLS extension
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pass
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@ -92,78 +132,94 @@ def _smtp_ehlo_tls(smtp: SMTP, helo_host: str):
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# SSL/TLS support is not available to your Python interpreter
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pass
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def _smtp_mail(smtp: SMTP, from_address: EmailAddress):
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'Send and evaluate the `MAIL FROM` command.'
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code, message = smtp.mail(sender=from_address.ace)
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if code >= 400:
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# MAIL FROM bails out, no further SMTP commands are acceptable
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raise _ProtocolError('MAIL FROM', code, message)
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def _smtp_converse(
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mx_record: str, smtp_timeout: int, debug: bool, helo_host: str,
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from_address: EmailAddress, email_address: EmailAddress
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) -> Tuple[int, str]:
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def mail(self, *args, **kwargs):
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"""
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Do the `SMTP` conversation with one MX, and return code and message
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of the reply to the `RCPT TO:` command.
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If the conversation fails before the `RCPT TO:` command can be
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issued, a `_ProtocolError` is raised.
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Like `smtplib.SMTP.mail`, but raise an appropriate exception on
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negative SMTP server response.
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"""
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if debug:
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LOGGER.debug(msg=f'Trying {mx_record} ...')
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with SMTP(timeout=smtp_timeout) as smtp:
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smtp._host = mx_record # Workaround for bug in smtplib
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smtp.set_debuglevel(debuglevel=2 if debug else False)
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code, message = smtp.connect(host=mx_record)
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code, message = super().mail(*args, **kwargs)
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if code >= 400:
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raise _ProtocolError('connect', code, message)
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_smtp_ehlo_tls(smtp=smtp, helo_host=helo_host)
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_smtp_mail(smtp=smtp, from_address=from_address)
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return smtp.rcpt(recip=email_address.ace)
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raise SMTPResponseException(code, message)
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return code, message
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def _check_mx_records(
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mx_records: list, smtp_timeout: int, helo_host: str,
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from_address: EmailAddress, email_address: EmailAddress,
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debug: bool, raise_communication_errors: bool,
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raise_temporary_errors: bool) -> Optional[bool]:
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'Check the mx records for a given email address.'
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communication_errors = {}
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temporary_errors = {}
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for mx_record in mx_records:
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try:
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code, message = _smtp_converse(
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mx_record=mx_record, smtp_timeout=smtp_timeout, debug=debug,
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helo_host=helo_host, from_address=from_address,
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email_address=email_address)
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def rcpt(self, *args, **kwargs):
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"""
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Like `smtplib.SMTP.rcpt`, but handle negative SMTP server
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responses directly.
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"""
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code, message = super().rcpt(*args, **kwargs)
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if code >= 500:
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# Address clearly invalid: exit early.
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raise AddressNotDeliverableError({mx_record: (
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# Address clearly invalid: issue negative result
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raise AddressNotDeliverableError({self._host: (
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'RCPT TO', code, message.decode(errors='ignore'))})
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elif code >= 400:
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# Temporary error on this MX: collect message and continue.
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temporary_errors[mx_record] = (
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# Temporary error on this host: collect message
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self.__temporary_errors[self._host] = (
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'RCPT TO', code, message.decode(errors='ignore'))
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else:
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# Address clearly valid: exit early.
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return code, message
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def quit(self):
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"""
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Like `smtplib.SMTP.quit`, but make sure that everything is
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cleaned up properly even if the connection has been lost before.
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"""
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try:
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return super().quit()
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except SMTPServerDisconnected:
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self.ehlo_resp = self.helo_resp = None
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self.esmtp_features = {}
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self.does_esmtp = False
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self.close()
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def _check_one(self, host: str) -> bool:
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"""
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Run the check for one SMTP server. On positive result, return
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`True`. On negative result, raise `AddressNotDeliverableError`.
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On ambiguous result (4xx response to `RCPT TO`) or any
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communication issue before even reaching `RCPT TO` in the
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protocol, collect error message for later use and return
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`False`.
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"""
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try:
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self.connect(host)
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self.starttls()
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self.ehlo_or_helo_if_needed()
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self.mail(self.__sender)
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code, message = self.rcpt(self.__recip)
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except SMTPServerDisconnected as e:
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self.__communication_errors[self._host] = (
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self.__command, 0, str(e))
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return False
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except SMTPResponseException as e:
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self.__communication_errors[self._host] = (
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self.__command, e.smtp_code,
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e.smtp_error.decode(errors='ignore'))
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return False
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finally:
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self.quit()
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return (code < 400)
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def check(self, hosts: List[str]) -> Optional[bool]:
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"""
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Run the check for all given SMTP servers. On positive result,
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return `True`. On negative result, raise
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`AddressNotDeliverableError`. On ambiguous result (4xx
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response(s) to `RCPT TO`) or any communication issue(s) before
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even reaching `RCPT TO` in the protocol, either raise an
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exception or return `None` depending on the parameters.
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"""
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for host in hosts:
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if self.debuglevel > 0:
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LOGGER.debug(msg=f'Trying {host} ...')
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if self._check_one(host):
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return True
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except (SocketError, SMTPServerDisconnected) as error:
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# Connection problem: collect message and continue.
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communication_errors[mx_record] = ('connect', 0, error)
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except _ProtocolError as error:
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# SMTP communication error: collect message and continue.
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communication_errors[mx_record] = (
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error.command, error.code, error.message)
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# Raise exceptions on ambiguous results if desired. If in doubt, raise the
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# CommunicationError because that one might point to local configuration or
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# blacklisting issues.
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if communication_errors and raise_communication_errors:
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raise SMTPCommunicationError(communication_errors)
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if temporary_errors and raise_temporary_errors:
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raise SMTPTemporaryError(temporary_errors)
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# Raise exceptions on ambiguous results if desired. If in doubt, raise
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# the CommunicationError because that one might point to local
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# configuration or blacklisting issues.
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if self.__communication_errors and self.__raise_communication_errors:
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raise SMTPCommunicationError(self.__communication_errors)
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if self.__temporary_errors and self.__raise_temporary_errors:
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raise SMTPTemporaryError(self.__temporary_errors)
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# Can't verify whether or not email address exists.
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return None
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@ -204,7 +260,6 @@ def mx_check(
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exceptions is raised depending on the exact issue, all derived from
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`MXError`.
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"""
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host = helo_host or gethostname()
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from_address = from_address or email_address
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if email_address.domain_literal_ip:
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mx_records = [email_address.domain_literal_ip]
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@ -213,8 +268,9 @@ def mx_check(
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domain=email_address.domain, timeout=dns_timeout)
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if skip_smtp:
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return True
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return _check_mx_records(
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mx_records=mx_records, smtp_timeout=smtp_timeout, helo_host=host,
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from_address=from_address, email_address=email_address, debug=debug,
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smtp_checker = _SMTPChecker(
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local_hostname=helo_host, timeout=smtp_timeout, debug=debug,
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raise_communication_errors=raise_communication_errors,
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raise_temporary_errors=raise_temporary_errors)
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raise_temporary_errors=raise_temporary_errors,
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sender=from_address.ace, recip=email_address.ace)
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return smtp_checker.check(mx_records)
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