Django

1 Keep the key on the server

MAILVET_KEY=mv_live_your_key

Set it wherever your server reads its environment. Never put it in client code.

2 Install requests

pip install requests

3 Put the check in one place

accounts/mailvet.py

import logging
import os

import requests

log = logging.getLogger(__name__)


def check_email(email):
    # Returns MailVet's answer, or None if there is no answer.
    try:
        r = requests.get(
            "https://mailvet.dev/v1/check",
            params={"email": email},
            headers={"Authorization": f"Bearer {os.environ['MAILVET_KEY']}"},
            timeout=5,
        )
        r.raise_for_status()
        return r.json()
    except (requests.RequestException, KeyError, ValueError) as err:
        log.warning("mailvet: no answer: %s", err)
        return None

4 Use it in the form

accounts/forms.py

from django import forms
from django.core.exceptions import ValidationError

from .mailvet import check_email


class SignupForm(forms.Form):
    email = forms.EmailField()

    def clean_email(self):
        email = self.cleaned_data["email"]
        check = check_email(email)
        if check is None:
            return email  # a signup shouldn't die because of us

        if check["did_you_mean"]:
            local = email.rpartition("@")[0]
            raise ValidationError(
                f"Did you mean {local}@{check['did_you_mean']}?",
                code="typo",
            )
        if check["verdict"] == "invalid":
            raise ValidationError("That address can't receive mail.", code="invalid")
        if check["verdict"] == "risky" and check["disposable"]:
            raise ValidationError(
                "Please use a permanent address, not a throwaway one.",
                code="disposable",
            )
        return email