Verify emails in Flask with Verifly

Why verify emails server-side in Flask

Flask gives you a thin, explicit request cycle, which is exactly where an email check belongs. The signup route is the highest-value place to catch a bad address: it is the last moment before you create a user, send a confirmation, and start building sender reputation on that mailbox. WTForms or a regex validator only confirm that user@dead-domain.com looks like an email — they cannot tell you the mailbox bounces. Verifly performs a live SMTP probe over one HTTPS call and tells you the truth.

The check must run server-side. Your Verifly key is a Bearer secret, so it belongs in an environment variable read inside the view, never in a template or client-side JavaScript. A single requests.get against /api/v1/verify inside the route returns a JSON verdict with a result field of deliverable, undeliverable, or risky plus boolean flags for disposable, role, catch_all, and smtp. Branch on those to reject throwaway domains and dead mailboxes right there in the handler.

Pricing fits a Flask app cleanly: no seat to justify, just credits from $2 per 1,000 checks down to $0.60 per 1,000 at volume. Self-register for 100 free credits with no card at the autonomous register endpoint and drop the key into your config.

Fail open so a network blip never blocks signup

The one rule that keeps a verification step from becoming an outage: fail open. If Verifly is briefly unreachable or slow, you never want a legitimate user turned away at registration. Wrap the call in a try/except with a short timeout and, on any RequestException, let the signup proceed. You trade a rare unverified address for never blocking a real customer — the right bargain at the front door.

import requests

VERIFLY_KEY = "vf_YOUR_KEY"

def email_is_acceptable(email: str) -> bool:
    """Return False only when we KNOW the address is bad."""
    try:
        r = requests.get(
            "https://verifly.email/api/v1/verify",
            params={"email": email},
            headers={"Authorization": f"Bearer {VERIFLY_KEY}"},
            timeout=8,
        )
        data = r.json()
    except requests.RequestException:
        return True  # fail open: never block signup on a network error

    if data.get("disposable") or data.get("role"):
        return False
    return data["result"] != "undeliverable"

Batch-clean a list from a Flask admin action

Beyond the signup route, Flask apps often need to clean an imported list — leads pasted into an admin form, a CSV upload, or rows pulled from your own database. Do not loop the single endpoint; send them together to POST /api/v1/verify/batch. It accepts a JSON body with an emails array and returns a results array in the same order, so you can zip it back against your source rows and keep only the deliverable ones.

import requests
from flask import request, jsonify

@app.post("/admin/clean-list")
def clean_list():
    emails = request.json["emails"]  # e.g. ["a@x.com", "b@y.com", ...]
    r = requests.post(
        "https://verifly.email/api/v1/verify/batch",
        json={"emails": emails},
        headers={
            "Authorization": f"Bearer {VERIFLY_KEY}",
            "Content-Type": "application/json",
        },
        timeout=30,
    )
    results = r.json()["results"]
    deliverable = [x["email"] for x in results if x["result"] == "deliverable"]
    return jsonify(kept=deliverable, total=len(results))