[FIXED] Flask: flask_mail never sends email (Hangs without response)

Issue

I have the following code:

Blueprint file snippet:

...
from flask_mail import Message
from app import mail
from os import environ
...

@index_bp.route('/contact', methods=['POST'])
def contact():
    form = ContactForm()
    
    if form.validate_on_submit():
        print('Form received')
        msg = Message('Test', recipients=environ.get('TARGET_MAIL'))
        print('msg created')
        msg.body = 'Test mail'
        print('Body created')
        mail.send(msg)
        print('Mail sent')

    
    return redirect(url_for('.index'))

Config file:

class Config:
    STATIC_FOLDER = 'static'
    TEMPLATES_FOLDER = 'templates'
    SECRET_KEY = environ.get('SECRET_KEY')
    MAIL_SERVER = 'smtp.google.com'
    MAIL_PORT = 465
    MAIL_USERNAME = environ.get('MAIL_USERNAME')
    MAIL_PASSWORD = environ.get('MAIL_PASSWORD')
    MAIL_USE_TLS = False
    MAIL_USE_SSL = True
    MAIL_DEFAULT_SENDER = environ.get('MAIL_USERNAME')

init file:

from flask import Flask
from flask_mail import Mail

mail = Mail()
def init_app():
    # Set up core app
    app = Flask(__name__)
    app.config.from_object('config.Config')
    mail.init_app(app)
    
    with app.app_context():
        # Import app routes
        from .index import routes

        # Register blueprints
        app.register_blueprint(routes.index_bp)

        return app

When I attempt to test the email functionality of the app, the mail.send(...) part just hands up. It never resolves, effectively not raising any errors but leaving the page loading forever. Most likely it has to do with Gmail, but I have no clue what is missing.

Any help is highly appreciated. Here are the prints the code generates:

Form received

msg created

Body created

proceeds to avoid doing anything else leaving the page loading

** Update **

Here is another snippet I made for the sole purpose of testing Flask Mail with Gmail and still got the same error:

from flask import Flask
from flask_mail import Mail, Message

app = Flask(__name__)

app.config['MAIL_SERVER']='smtp.google.com'
app.config['MAIL_PORT'] = 465
app.config['MAIL_USERNAME'] = '<new gmail account>@gmail.com'
app.config['MAIL_PASSWORD'] = '<app password>'
app.config['MAIL_USE_TLS'] = False
app.config['MAIL_USE_SSL'] = True

mail = Mail(app)

@app.route("/")
def index():
  msg = Message('Hello from the other side!', sender = '<new gmail account>@gmail.com', recipients = ['<my gmail address>@gmail.com'])
  msg.body = "This is a test email"
  mail.send(msg)
  return "Message sent!"

Edit:

The error was using smtp.google.com instead of smtp.gmail.com, however, the answer posted here helped a lot as well :).

Solution

It because of your Google account, Google recently change some security features that don't let less secure apps to signing in to your account with just username and password, You can use app password in MAIL_PASSWORD configuration instead of your Google account password to solve the problem

in the link below, I answer the same question you can check it

Google disabled access to less secure apps

Answered By - Mohammad Reza Aram