How to block disposable emails in Django

# accounts/validators.py
import requests
from django.core.cache import cache
from django.core.exceptions import ValidationError

LOOKUP_URL = "https://usevetto.com/v1/audit"
DEAD = {"nxdomain", "no_mx_a", "null_mx", "no_mail"}


def validate_not_disposable(email):
    if "@" not in (email or ""):
        return  # EmailField reports malformed addresses
    domain = email.rsplit("@", 1)[1].strip().lower()

    key = f"vetto:domain:{domain}"
    result = cache.get(key)
    if result is None:
        try:
            response = requests.post(LOOKUP_URL, json={"domains": [domain]}, timeout=2)
            result = (response.json().get("results") or {}).get(domain)
        except (requests.RequestException, ValueError):
            return  # timeout, network error or bad JSON: fail open
        if result is None:
            return  # rate limited or no answer: fail open, don't cache
        cache.set(key, result, 60 * 60 * 24)  # one lookup per domain per day

    if result.get("disposable"):
        raise ValidationError(
            "Please use a permanent email address. Temporary inboxes are not accepted.",
            code="disposable_email",
        )
    if result.get("status") in DEAD:
        raise ValidationError(
            "This email domain cannot receive mail. Please check it for typos.",
            code="dead_email_domain",
        )

# accounts/forms.py
from django import forms
from django.contrib.auth.forms import UserCreationForm
from django.contrib.auth.models import User

from .validators import validate_not_disposable


class SignupForm(UserCreationForm):
    email = forms.EmailField(required=True, validators=[validate_not_disposable])

    class Meta(UserCreationForm.Meta):
        model = User
        fields = ("username", "email")

# accounts/adapter.py
from allauth.account.adapter import DefaultAccountAdapter

from .validators import validate_not_disposable


class AccountAdapter(DefaultAccountAdapter):
    def clean_email(self, email):
        email = super().clean_email(email)
        validate_not_disposable(email)  # raises ValidationError
        return email


# settings.py
ACCOUNT_ADAPTER = "accounts.adapter.AccountAdapter"

# accounts/serializers.py
from rest_framework import serializers

from .validators import validate_not_disposable


class RegisterSerializer(serializers.Serializer):
    email = serializers.EmailField(validators=[validate_not_disposable])
    password = serializers.CharField(write_only=True, min_length=8)

# accounts/tests.py
from unittest import mock

import requests
from django.core.cache import cache
from django.core.exceptions import ValidationError
from django.test import SimpleTestCase

from .validators import validate_not_disposable


def answer(domain, **result):
    response = mock.Mock()
    response.json.return_value = {"ok": True, "results": {domain: {"mx": [], "disposable": False, **result}}}
    return response


class NotDisposableTests(SimpleTestCase):
    def setUp(self):
        cache.clear()

    @mock.patch("accounts.validators.requests.post")
    def test_rejects_throwaway(self, post):
        post.return_value = answer("mailinator.com", status="skipped", disposable=True)
        with self.assertRaises(ValidationError):
            validate_not_disposable("x7@mailinator.com")

    @mock.patch("accounts.validators.requests.post", side_effect=requests.Timeout)
    def test_fails_open(self, post):
        validate_not_disposable("jane@slow.example")  # no exception