content: from threading import Thread
  from flask import current_app
  from flask_mail import Message
  from app import mail
  
  
  def send_async_email(app, msg):
      with app.app_context():
          mail.send(msg)
  
  
  def send_email(subject, sender, recipients, text_body, html_body,
                 attachments=None, sync=False):
      msg = Message(subject, sender=sender, recipients=recipients)
      msg.body = text_body
      msg.html = html_body
      if attachments:
          for attachment in attachments:
              msg.attach(*attachment)
      if sync:
          mail.send(msg)
      else:
          Thread(target=send_async_email,
                 args=(current_app._get_current_object(), msg)).start()
  