Flask Mail ConnectionResetError: [Errno 54] Connection reset by peer - email

Question

I am following this basic tutorial from the link exactly:
https://www.tutorialspoint.com/flask/flask_mail.htm
Anyone know what cause this problem? I think it should be a common problem?
Is there any additional setting for flask mail?
Here is the full error msg:
Traceback (most recent call last):
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1997, in __call__
return self.wsgi_app(environ, start_response)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1985, in wsgi_app
response = self.handle_exception(e)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1540, in handle_exception
reraise(exc_type, exc_value, tb)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/_compat.py", line 33, in reraise
raise value
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1982, in wsgi_app
response = self.full_dispatch_request()
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1614, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1517, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/_compat.py", line 33, in reraise
raise value
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1612, in full_dispatch_request
rv = self.dispatch_request()
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1598, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/Users/boxia/PycharmProjects/learn_flask/test.py", line 18, in index
mail.send(msg)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask_mail.py", line 491, in send
with self.connect() as connection:
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask_mail.py", line 144, in __enter__
self.host = self.configure_host()
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask_mail.py", line 156, in configure_host
host = smtplib.SMTP_SSL(self.mail.server, self.mail.port)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/smtplib.py", line 1029, in __init__
source_address)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/smtplib.py", line 251, in __init__
(code, msg) = self.connect(host, port)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/smtplib.py", line 335, in connect
self.sock = self._get_socket(host, port, self.timeout)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/smtplib.py", line 1037, in _get_socket
server_hostname=self._host)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/ssl.py", line 401, in wrap_socket
_context=self, _session=session)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/ssl.py", line 808, in __init__
self.do_handshake()
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/ssl.py", line 1061, in do_handshake
self._sslobj.do_handshake()
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/ssl.py", line 683, in do_handshake
self._sslobj.do_handshake()