How to Use an Email Validation Service for Flask User Authentication

User authentication is a critical component of nearly every web application. Allowing users to register an account and securely log in enables personalization, access control, and many other important features. However, with user registration comes the challenge of ensuring the integrity of user-provided data – especially email addresses.

Email addresses serve as a unique identifier for user accounts and are key for communication. Therefore, it‘s crucial to make sure email addresses provided during registration are valid and actually belong to the user. Accepting invalid, disposable, or fraudulent email addresses can lead to security issues, transactional email failures, and degraded user experience.

This is where an email validation service comes to the rescue. By integrating an email validation API into your registration flow, you can automatically check the validity and authenticity of user-provided email addresses in real-time. This not only streamlines the registration process but enhances the security and reliability of your app.

In this post, we‘ll walk through how to add email validation to a Flask app using the popular email validation service Abstract API. We‘ll cover the basics of Flask user authentication, integrating the email validation API, and additional use cases and benefits.

Understanding Email Validation Services

Before diving into the code, let‘s review how email validation services work and what benefits they provide.

An email validation service inspects an email address and determines its validity, authenticity, and risk level. This is done by checking the email address against a variety of factors, including:

• Syntax and formatting
• DNS records
• Mailbox existence
• Disposable email provider lists
• Fraudulent email patterns
• Spam trap indicators

Based on these checks, the service will return a validity score or status for the email address. A high validity score means the email is properly formatted, the domain exists and accepts mail, and the specific mailbox is live. A low score indicates a problematic address that is likely invalid, disposable, or associated with fraud.

By validating email addresses, you gain several key benefits:

1. Improved data quality – Ensure only valid and authentic emails enter your database
2. Fraud prevention – Block fake signups and fraudulent activity via disposable emails
3. Increased deliverability – Avoid hard bounces and protect sender reputation
4. Better user experience – Catch typos and suggest corrections in real-time

With this context in mind, let‘s see how to put email validation into practice in a Flask app.

Setting Up Flask User Authentication

As a starting point, we‘ll create a basic Flask app with user registration and login functionality. We‘ll use the popular Flask-Login extension for session management and the Flask-WTF extension for form handling.

First, make sure you have Python and pip installed. Create a new directory for the project and set up a virtual environment:

$ mkdir flask-email-validation
$ cd flask-email-validation
$ python3 -m venv venv
$ . venv/bin/activate

Next, install the necessary dependencies:

$ pip install flask flask-login flask-wtf

Now let‘s create the basic structure of the Flask app. Create a file called app.py with the following contents:

from flask import Flask, render_template, redirect, url_for
from flask_login import LoginManager, UserMixin, login_user, logout_user, login_required
from flask_wtf import FlaskForm
from wtforms import StringField, PasswordField, SubmitField
from wtforms.validators import DataRequired, Email

app = Flask(__name__)
app.secret_key = ‘super-secret-key‘

# Configure Flask-Login
login_manager = LoginManager()
login_manager.init_app(app)

# Mock user database
users = {
    ‘[email protected]‘: {‘password‘: ‘password123‘}
}

# User model
class User(UserMixin):
    pass

@login_manager.user_loader
def user_loader(email):
    if email not in users:
        return

    user = User()
    user.id = email
    return user

# Login form
class LoginForm(FlaskForm):
    email = StringField(‘Email‘, validators=[DataRequired(), Email()])
    password = PasswordField(‘Password‘, validators=[DataRequired()])
    submit = SubmitField(‘Log In‘)

# Registration form 
class RegisterForm(FlaskForm):
    email = StringField(‘Email‘, validators=[DataRequired(), Email()])
    password = PasswordField(‘Password‘, validators=[DataRequired()])
    submit = SubmitField(‘Register‘)

# Routes

@app.route(‘/‘)
def home():
    return render_template(‘home.html‘)

@app.route(‘/register‘, methods=[‘GET‘, ‘POST‘])
def register():
    form = RegisterForm()
    if form.validate_on_submit():
        email = form.email.data
        password = form.password.data

        # TODO: Validate email using email validation service

        # Add user to database
        users[email] = {‘password‘: password}
        return redirect(url_for(‘login‘))

    return render_template(‘register.html‘, form=form)

@app.route(‘/login‘, methods=[‘GET‘, ‘POST‘])
def login():
    form = LoginForm()
    if form.validate_on_submit():
        email = form.email.data
        password = form.password.data

        if email in users and users[email][‘password‘] == password:
            user = User()
            user.id = email
            login_user(user)
            return redirect(url_for(‘home‘))

    return render_template(‘login.html‘, form=form)

@app.route(‘/logout‘)
@login_required
def logout():
    logout_user()
    return redirect(url_for(‘home‘))

if __name__ == ‘__main__‘:
    app.run(debug=True)

This sets up a basic Flask app with user registration, login, and logout routes. The registration form collects an email and password, but doesn‘t actually validate the email yet. The login form authenticates the user against a mock user database.

Next, create a templates directory and add the following HTML templates:

templates/home.html:

{% extends "layout.html" %}

{% block content %}


  {% if current_user.is_authenticated %}
    <p>You are logged in as {{ current_user.id }}</p>
    <a href="{{ url_for(‘logout‘) }}">Log Out</a>
  {% else %}
    <p>You are not logged in.</p>
    <a href="{{ url_for(‘login‘) }}">Log In</a>
    <a href="{{ url_for(‘register‘) }}">Register</a>
  {% endif %}

{% endblock %}

templates/layout.html:

<!doctype html>
<html>
  <head>
    <title>Flask Email Validation Demo</title>
  </head>
  <body>
    {% block content %}
    {% endblock %}
  </body>
</html>

templates/login.html:

{% extends "layout.html" %}

{% block content %}
  <h2>Log In</h2>
  <form method="POST">
    {{ form.csrf_token }}
    {{ form.email.label }} {{ form.email() }}
    {{ form.password.label }} {{ form.password() }}
    {{ form.submit() }}
  </form>
{% endblock %}

templates/register.html:

{% extends "layout.html" %}

{% block content %}
  <h2>Register</h2>
  <form method="POST">
    {{ form.csrf_token }}
    {{ form.email.label }} {{ form.email() }}
    {{ form.password.label }} {{ form.password() }} 
    {{ form.submit() }}
  </form>
{% endblock %}

At this point, you should have a working Flask app with basic user registration and login. You can run the app with:

$ flask run

Visit http://localhost:5000 in your browser and test the registration and login flows. The app will accept any email address, so you could register with something invalid like fakeuser@invaliddomain without any error.

In the next section, we‘ll add email validation to prevent invalid or fraudulent signups.

Integrating an Email Validation Service

Now that we have a basic Flask user registration system, let‘s integrate an email validation service to check the validity of emails provided during signup. We‘ll use the email validation API from Abstract API in this example.

First, sign up for a free account at Abstract API. Once you‘ve created an account, you‘ll get an API key.

Next, install the requests library to make HTTP requests to the API:

$ pip install requests

Now let‘s create a helper function to validate an email using the Abstract API service. Create a new file called validation.py with the following contents:

import requests

def validate_email(email):
    api_key = ‘YOUR_API_KEY‘  
    response = requests.get(
        ‘https://emailvalidation.abstractapi.com/v1/‘,
        params = {‘api_key‘: api_key, ‘email‘: email}
    )

    return response.json()[‘deliverability‘] == ‘DELIVERABLE‘

This function takes an email address, sends it to the Abstract API email validation endpoint, and returns True if the email is deliverable or False if it‘s undeliverable, risky, or invalid.

Be sure to replace YOUR_API_KEY with your actual API key.

With the validation helper in place, let‘s integrate it into the registration flow. Open app.py and make the following changes:

First, import the validate_email function at the top of the file:

from validation import validate_email

Then, in the register route, call validate_email before adding the user to the database:

@app.route(‘/register‘, methods=[‘GET‘, ‘POST‘])
def register():
    form = RegisterForm()
    if form.validate_on_submit():
        email = form.email.data
        password = form.password.data

        if not validate_email(email):
            form.email.errors.append(‘Invalid email address!‘)
            return render_template(‘register.html‘, form=form)

        users[email] = {‘password‘: password}
        return redirect(url_for(‘login‘))

    return render_template(‘register.html‘, form=form)

Now when a user submits the registration form, their email will be validated before creating the account. If the email is invalid, an error message is added to the form and re-rendered.

Let‘s test it out. Run the Flask app again with flask run and visit the registration page. Try submitting different email addresses and see the results:

• A valid email like [email protected] should work and create the account
• An invalid email like fakeuser@invaliddomain should show an error message
• A disposable email like [email protected] should also be rejected

With these changes, our Flask app is now performing real-time email validation during registration! This ensures a higher quality of user signups and prevents fraud or invalid data from polluting the database.

Additional Use Cases and Benefits

Beyond registration forms, there are many other use cases for email validation services:

1. Newsletter signups – Ensure subscribers provide real, active email addresses to maintain good deliverability rates.

2. Checkout forms – Prevent typos or fake emails that could disrupt order confirmations and shipping updates.

3. User invitations – For invite-only apps, validate recipient emails before sending invitation codes.

4. Feedback or contact forms – Filter out invalid emails to avoid undeliverable responses and spam.

In each situation, email validation helps maintain data integrity, avoid hard bounces, and provide a better user experience. Typos can be caught and fixed in real-time, while fraudulent signups can be blocked entirely.

Email validation also improves security by making it harder to create fake accounts or automate attacks. Many attackers rely on using disposable or generated email addresses to bypass registration restrictions.

Conclusion

Proper email validation is a small but critical step in creating a secure and reliable web application. Adding an email validation service to your Flask registration flow is a straightforward process that can pay dividends in data quality, security, and user experience.

By using an API service like Abstract API, validating emails can be done with just a few lines of code. The service handles all the complex validations and keeps the list of disposable email providers up to date.

While this post focused on Flask, the same principles apply to any web framework or language. If your application involves user emails in any way, consider using an email validation service to ensure you‘re working with real, deliverable addresses.