Flask: Why should i get this error {smtplib.SMTPServerDisconnected: please run connect() first)} if i down everything right

Question

config.py file:

MAIL_SERVER   = os.environ.get(\'MAIL_SERVER\')
MAIL_PORT     = int(os.environ.get(\'MAIL_PORT\') or 25)
MAIL_USE_TLS  = os.e