FastAPI

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 httpx

pip install fastapi httpx

3 The dependency and the route

main.py

import logging
import os
from typing import Annotated

import httpx
from fastapi import Depends, FastAPI, HTTPException
from pydantic import BaseModel

log = logging.getLogger(__name__)
app = FastAPI()


class Signup(BaseModel):
    email: str


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


async def vetted_email(body: Signup) -> str:
    email = body.email.strip()
    check = await 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 HTTPException(422, f"Did you mean {local}@{check['did_you_mean']}?")
    if check["verdict"] == "invalid":
        raise HTTPException(422, "That address can't receive mail.")
    if check["verdict"] == "risky" and check["disposable"]:
        raise HTTPException(422, "Please use a permanent address, not a throwaway one.")
    return email


@app.post("/signup", status_code=201)
async def signup(email: Annotated[str, Depends(vetted_email)]):
    # Create the user here.
    return {"email": email}