flask-mail gmail: connection refused

As far as I can tell there is nothing wrong with this configuration. The only problem is that your application is not using it. You should update configuration before you initialize Mail:

app = Flask(__name__)

app.config.update(dict(
    DEBUG = True,
    MAIL_SERVER = 'smtp.gmail.com',
    MAIL_PORT = 587,
    MAIL_USE_TLS = True,
    MAIL_USE_SSL = False,
    MAIL_USERNAME = '[email protected]',
    MAIL_PASSWORD = 'my_password',
))

mail = Mail(app)

In addition to zero323's answer, adding the configuration before creating a Mail object should help, but if it gives an SMTPAuthentication error with a gmail server, then just for testing purpose one may allow less secure apps to login for a while - https://myaccount.google.com/security#signin