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from typing import Optional, Any, Dict
from .exceptions_types import EmailUndeliverableError
import dns.resolver
import dns.exception
def caching_resolver(*, timeout: Optional[int] = None, cache=None, dns_resolver=None):
if timeout is None:
from . import DEFAULT_TIMEOUT
timeout = DEFAULT_TIMEOUT
resolver = dns_resolver or dns.resolver.Resolver()
resolver.cache = cache or dns.resolver.LRUCache() # type: ignore
resolver.lifetime = timeout # type: ignore # timeout, in seconds
return resolver
def validate_email_deliverability(domain: str, domain_i18n: str, timeout: Optional[int] = None, dns_resolver=None):
# Check that the domain resolves to an MX record. If there is no MX record,
# try an A or AAAA record which is a deprecated fallback for deliverability.
# Raises an EmailUndeliverableError on failure. On success, returns a dict
# with deliverability information.
# If no dns.resolver.Resolver was given, get dnspython's default resolver.
# Override the default resolver's timeout. This may affect other uses of
# dnspython in this process.
if dns_resolver is None:
from . import DEFAULT_TIMEOUT
if timeout is None:
timeout = DEFAULT_TIMEOUT
dns_resolver = dns.resolver.get_default_resolver()
dns_resolver.lifetime = timeout
elif timeout is not None:
raise ValueError("It's not valid to pass both timeout and dns_resolver.")
deliverability_info: Dict[str, Any] = {}
try:
try:
# Try resolving for MX records (RFC 5321 Section 5).
response = dns_resolver.resolve(domain, "MX")
# For reporting, put them in priority order and remove the trailing dot in the qnames.
mtas = sorted([(r.preference, str(r.exchange).rstrip('.')) for r in response])
# RFC 7505: Null MX (0, ".") records signify the domain does not accept email.
# Remove null MX records from the mtas list (but we've stripped trailing dots,
# so the 'exchange' is just "") so we can check if there are no non-null MX
# records remaining.
mtas = [(preference, exchange) for preference, exchange in mtas
if exchange != ""]
if len(mtas) == 0: # null MX only, if there were no MX records originally a NoAnswer exception would have occurred
raise EmailUndeliverableError(f"The domain name {domain_i18n} does not accept email.")
deliverability_info["mx"] = mtas
deliverability_info["mx_fallback_type"] = None
except dns.resolver.NoAnswer:
# If there was no MX record, fall back to an A record. (RFC 5321 Section 5)
try:
response = dns_resolver.resolve(domain, "A")
deliverability_info["mx"] = [(0, str(r)) for r in response]
deliverability_info["mx_fallback_type"] = "A"
except dns.resolver.NoAnswer:
# If there was no A record, fall back to an AAAA record.
# (It's unclear if SMTP servers actually do this.)
try:
response = dns_resolver.resolve(domain, "AAAA")
deliverability_info["mx"] = [(0, str(r)) for r in response]
deliverability_info["mx_fallback_type"] = "AAAA"
except dns.resolver.NoAnswer as e:
# If there was no MX, A, or AAAA record, then mail to
# this domain is not deliverable, although the domain
# name has other records (otherwise NXDOMAIN would
# have been raised).
raise EmailUndeliverableError(f"The domain name {domain_i18n} does not accept email.") from e
# Check for a SPF (RFC 7208) reject-all record ("v=spf1 -all") which indicates
# no emails are sent from this domain (similar to a Null MX record
# but for sending rather than receiving). In combination with the
# absence of an MX record, this is probably a good sign that the
# domain is not used for email.
try:
response = dns_resolver.resolve(domain, "TXT")
for rec in response:
value = b"".join(rec.strings)
if value.startswith(b"v=spf1 "):
deliverability_info["spf"] = value.decode("ascii", errors='replace')
if value == b"v=spf1 -all":
raise EmailUndeliverableError(f"The domain name {domain_i18n} does not send email.")
except dns.resolver.NoAnswer:
# No TXT records means there is no SPF policy, so we cannot take any action.
pass
except dns.resolver.NXDOMAIN as e:
# The domain name does not exist --- there are no records of any sort
# for the domain name.
raise EmailUndeliverableError(f"The domain name {domain_i18n} does not exist.") from e
except dns.resolver.NoNameservers:
# All nameservers failed to answer the query. This might be a problem
# with local nameservers, maybe? We'll allow the domain to go through.
return {
"unknown-deliverability": "no_nameservers",
}
except dns.exception.Timeout:
# A timeout could occur for various reasons, so don't treat it as a failure.
return {
"unknown-deliverability": "timeout",
}
except EmailUndeliverableError:
# Don't let these get clobbered by the wider except block below.
raise
except Exception as e:
# Unhandled conditions should not propagate.
raise EmailUndeliverableError(
"There was an error while checking if the domain name in the email address is deliverable: " + str(e)
) from e
return deliverability_info
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