Flask-Mail [SSL: WRONG_VERSION_NUMBER] wrong version number (_ssl.c:1123)

Question

I'm developing a Flask application that implements a user registration system. The application uses Flask-Mail and itsdangerous to confirm a user's registration and reset their password via email. I configured Flask-Mail to use the recommended server settings provided by the email host that I'm using.

MAIL_PORT = 587
MAIL_USE_SSL = False
MAIL_USE_TLS = True

At first, things were working fine; I could submit emails without any issues. However, seemingly without changing any configuration settings, I now receive the following error when attempting to submit an email using Flask-Mail:

[SSL: WRONG_VERSION_NUMBER] wrong version number (_ssl.c:1123)

I'm not sure where the problem is, and I am wondering if something has changed on the email provider's end? I have tried setting MAIL_PORT = 25 with MAIL_USE_SSL=False and MAIL_USE_TLS=False; and, MAIL_PORT = 465 with MAIL_USE_SSL=True and MAIL_USE_TLS=False as well. Using the former, I receive the same error as with port 587, but using the latter I'm receiving STARTTLS extension not supported by server.

I'm running the Flask app in development mode at localhost:5000. Here's some of my configuration settings and code:

config.py

    SECRET_KEY = 'verysecret'
    MAIL_SERVER = "smtp.mymailservice.com"
    MAIL_PORT = 587
    MAIL_USE_SSL = False
    MAIL_USE_TLS = True
    MAIL_USERNAME = "[email protected]"
    MAIL_PASSWORD = "mypassword"
    MAIL_DEFAULT_SENDER = 'Brand <[email protected]>'

app/mailing.py

from flask_mail import Message
from flask import current_app
from .extensions import mail


def send_email(to, subject, template):
    msg = Message(
        subject,
        recipients=[to],
        html=template,
        sender=current_app.config["MAIL_DEFAULT_SENDER"]
    )
    mail.send(msg)

app/users/routes.py

(One of the routes where I receive the error)

from flask import (
    render_template, session, request, redirect, url_for, g, jsonify, flash
)

import uuid
from passlib.hash import sha256_crypt

from app.mailing import send_email
from app.extensions import db
from app.users import bp
from app.users.forms import *
from app.users.models import *
from app.users.token import *

@bp.route('/register', methods=['POST', 'GET'])
def register():

    # Initialize the Register Form
    form = RegisterForm()

    # If the submitted form is valid
    if form.validate_on_submit():

        # Check to see if a user already exists with this email address
        user = User.query.filter_by(email=form.email.data).first()

        # If there is not a user with this email address, create a new user
        if not user:
            new_user = User(public_id=str(uuid.uuid4()),
                            email=form.email.data,
                            password=sha256_crypt.encrypt(
                                (form.password.data)),
                            first_name=form.firstname.data,
                            last_name=form.lastname.data

                            )

            db.session.add(new_user)
            db.session.commit()

            token = generate_confirmation_token(new_user.email)
            confirm_url = url_for("users.confirm_email",
                                  token=token, _external=True)
            html = render_template('confirm_email.html',
                                   confirm_url=confirm_url)
            subject = "Please confirm your email"

            try:
                send_email(new_user.email, subject, html)
                flash("A confirmation email has been sent to you. Please verify your email address to activate your account.", category="success")
            except Exception as e:
                flash(
                    "There was a problem sending the confirmation email. Please try again later.", category="danger")
                print(e)

            session["user_id"] = new_user.public_id
            session["email"] = new_user.email
            session["name"] = new_user.first_name

            flash("Thanks for registering!", category="success")

            return redirect(url_for('users.unconfirmed'))
        else:
            flash("There is already an account associated with this email address. Log in, or use a different email address.")

    return render_template("register_user.html", form=form)

app/extensions.py

from flask_mail import Mail
from flask_bootstrap import Bootstrap
from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy()
bootstrap = Bootstrap()
mail = Mail()

app/init.py

from flask import Flask
from config import Config, DevelopmentConfig

from .errors import (
    page_not_found, forbidden, internal_server_error
)

from .extensions import (
    db, mail, bootstrap
)



def create_app(config_class=DevelopmentConfig):

    app = MyFlask(__name__)

    # Set Configuration
    app.config.from_object(config_class)
    
    # Register extensions
    # Initialize Boostrap-Flask
    bootstrap.init_app(app)

    # Initialize Flask-SQLAlchemy
    db.init_app(app)

    # Initialize Flask-Mail
    mail.init_app(app)

    # Register error views
    app.register_error_handler(404, page_not_found)
    app.register_error_handler(403, forbidden)
    app.register_error_handler(500, internal_server_error)

    with app.app_context():

        # register blueprints
        from app.main import bp as bp_main
        app.register_blueprint(bp_main)

        from app.users import bp as bp_users
        app.register_blueprint(bp_users)

        return app

Answer 1

This answer was almost there but not quite for me. Even more TL:DR.

Put this in your config.py file and forget about the rest...

class Config:
    MAIL_USE_TLS = True
    MAIL_USE_SSL = False

More details...

You probably have a config.py file that looks like this:

class Config:
    SECRET_KEY = os.environ.get('SECRET_KEY')
    SQLALCHEMY_DATABASE_URI = 'sqlite:///site.db' # os.environ.get('DATABASE_URI')
    MAIL_SERVER = os.environ.get('MAIL_SERVER')
    MAIL_PORT = os.environ.get('MAIL_PORT')
    MAIL_USE_TLS = os.environ.get('MAIL_USE_TLS')
    MAIL_USE_SSL = os.environ.get('MAIL_USE_SSL')
    MAIL_USERNAME = os.environ.get('MAIL_USERNAME')
    MAIL_PASSWORD = os.environ.get('MAIL_PASSWORD')
    MAIL_DEFAULT_SENDER = os.environ.get('MAIL_DEFAULT_SENDER')

And then you think you can have something like this in your VSCode debug config or the environment of your server:

"env": {
    "MAIL_USE_SSL":"true",
    "MAIL_USE_TLS":"true",

Well that doesn't work because of the answer from @serrobit because "true" in VSCode turns into a str instead of a Python True.

So back to the start, hard code TLS to True and SSL to False in the config.py file and go spend time on something useful.