[2019-01-21 03:07:51,954] ERROR in app: Exception on /register/ [POST]
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 2292, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1815, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1718, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1813, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1799, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "MyFlaskApp.py", line 131, in register
    mail.send(msg)
  File "/usr/local/lib/python2.7/site-packages/flask_mail.py", line 492, in send
    message.send(connection)
  File "/usr/local/lib/python2.7/site-packages/flask_mail.py", line 427, in send
    connection.send(self)
  File "/usr/local/lib/python2.7/site-packages/flask_mail.py", line 192, in send
    message.rcpt_options)
  File "/usr/lib64/python2.7/smtplib.py", line 737, in sendmail
    raise SMTPSenderRefused(code, resp, from_addr)
SMTPSenderRefused: (530, '5.5.1 Authentication Required. Learn more atn5.5.1  https://support.google.com/mail/?p=WantAuthError u186sm20332024pfu.51 - gsmtp', u'myemail@gmail.com')
IP.XX.XXX.XXX - - [21/Jan/2019 03:07:51] "POST /register/ HTTP/1.1" 500 -

app = Flask(__name__, static_url_path='/static')
app.config.update(
  DEBUG = False,
  MAIL_SERVER = 'smtp.gmail.com',
  MAIL_PORT = 465,
  MAIL_USE_SSL = True,
  MAIL_USERNAME = 'myemail@gmail.com',
  MAIL_DEFAULT_SENDER = 'myemail@gmail.com',
  MAIL_PASSWORD = 'GmailApplicationPassword',
  )
mail = Mail(app)

msg = Message("Welcome",
      sender = 'myemail@gmail.com',
      recipients = [request.form["email"]])
    msg.body = "Welcome! nn Congratulations on your successful registration. nn Cheers!"
    mail.send(msg)

$ pip freeze
Flask-Mail==0.9.1