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