old_contents: from flask_mail import Message
  
  from zou.app import mail
  
  
  def send_email(subject, body, recipient_email, html=None):
      """
      Send an email with given subject and body to given recipient.
      """
      if html is None:
          html = body
      message = Message(
          body=body,
          html=html,
          subject=subject,
          recipients=[recipient_email]
      )
      mail.send(message)
  
new_contents: from flask_mail import Message
  
  from zou.app import mail, app
  
  
  def send_email(subject, body, recipient_email, html=None):
      """
      Send an email with given subject and body to given recipient.
      """
      if html is None:
          html = body
      with app.app_context():
          message = Message(
              body=body,
              html=html,
              subject=subject,
              recipients=[recipient_email]
          )
          mail.send(message)
  
subject: Fix email sending in production environment