How to detect disposable emails in Python

May 16, 2026 · 6 min read

Disposable email addresses — temporary inboxes from services like mailinator.com — let users sign up without giving you a real address. In Python, you can reject them with a single function call. This guide covers Django, Flask, and FastAPI.

Install the package

The isdisposable package bundles 160,000+ disposable domains and runs offline — no API key, no network call, zero dependencies.

Terminalbash

pip install isdisposable

check.pypython

from isdisposable import is_disposable

is_disposable("test@mailinator.com")  # True
is_disposable("user@gmail.com")       # False

Django — a custom form validator

Wrap the check in a validator so it applies to any form or model field that holds an email.

validators.pypython

from django.core.exceptions import ValidationError
from isdisposable import is_disposable

def validate_not_disposable(value):
    if is_disposable(value):
        raise ValidationError(
            "Disposable email addresses are not allowed.",
            code="disposable",
        )

# In a form:
class SignupForm(forms.Form):
    email = forms.EmailField(validators=[validate_not_disposable])

Flask

app.pypython

from flask import Flask, request, jsonify
from isdisposable import is_disposable

app = Flask(__name__)

@app.post("/signup")
def signup():
    email = request.json["email"]
    if is_disposable(email):
        return jsonify(error="Disposable email addresses are not allowed."), 422
    # ...create the user
    return jsonify(ok=True)

FastAPI — a Pydantic validator

FastAPI validates request bodies with Pydantic. Add a field validator and the rejection happens before your route code even runs.

main.pypython

from fastapi import FastAPI
from pydantic import BaseModel, field_validator
from isdisposable import is_disposable

app = FastAPI()

class SignupRequest(BaseModel):
    email: str

    @field_validator("email")
    @classmethod
    def reject_disposable(cls, v: str) -> str:
        if is_disposable(v):
            raise ValueError("Disposable email addresses are not allowed.")
        return v

@app.post("/signup")
def signup(body: SignupRequest):
    # body.email is guaranteed non-disposable here
    return {"ok": True}

Cleaning an existing user table

Use is_disposable_bulk to audit a whole list at once and find accounts that slipped through before you added the check.

audit.pypython

from isdisposable import is_disposable_bulk

emails = [u.email for u in users]
flags = is_disposable_bulk(emails)

suspicious = [u for u, bad in zip(users, flags) if bad]
print(f"{len(suspicious)} disposable accounts found")

Catching brand-new domains

The offline list covers every known disposable domain. To also catch domains registered after your last update — plus MX-record checks and a risk score — use the API client:

api.pypython

from isdisposable import create_client

client = create_client(api_key="isd_live_xxxxx")
result = client.check("test@mailinator.com")
print(result.disposable, result.score)

See the API reference for the full response shape. Start with the free offline package and add the API only where you need live checks.