Reorganizing Flask Mail App

Hi everyone! I am working on setting up a web application using Flask. I want to be able to send users emails, like when they sign up for example. I followed a tutorial (Sending Emails with Flask - Step-by-Step Flask-Mail Guide | Mailtrap Blog - Sending emails in Flask) and it was working until I reorganized the code to be more than one file, which I need to do to make it work with the rest of my project. Since then, I am getting an error

File “C:\Flask Mail\service\routes.py”, line 6, in index
mail.send(msg)
NameError: name ‘mail’ is not defined

I am clearly doing something wrong, but I don’t know what. My file structure is like this:

Flask Mail
env
service
| pycache
| init.py
| extensions.py
| routes.py
run.py

My code looks like this:

    #__init__.py
    from flask import Flask
    from service import routes
    from .extensions import mail

    def create_app(config_file=None):
        # create and configure the app
        app = Flask(__name__)

        app.add_url_rule("/", view_func=routes.index)

        app.config['MAIL_SERVER']='sandbox.smtp.mailtrap.io'
        app.config['MAIL_PORT'] = 2525
        app.config['MAIL_USERNAME'] = <username from mailtrap>
        app.config['MAIL_PASSWORD'] = <password from mailtrap>
        app.config['MAIL_USE_TLS'] = True
        app.config['MAIL_USE_SSL'] = False

        mail.init_app(app)

        return app

    #extensions.py
    from flask_mail import Mail, Message
    mail = Mail()

    # routes.py
    from flask_mail import Message

    def index():
      msg = Message('Hello from the other side!', sender =   '[e-mail]', recipients = ['[e-mail]'])
      msg.body = "Hey Paul, sending you this email from my Flask app, lmk if it works"
      mail.send(msg)
      return "Message sent!"

    # run.py
    from service import create_app

    app = create_app()


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

What am I missing here?