input: 
  from celery import Celery
  from flask_mail import Message, Mail
  
  app = Celery('tasks', backend='redis://localhost')
  mail = Mail()
  
  @app.task
  def send_email(recipient_name, recipient_email, subject, message):
      """
      Create and send an email using Celery as a background task.
      >>> send_email('John Smith', 'john@example.com', 'Hello World', 'This is a test email.')
      None
      """
      msg = Message(subject, sender='example@example.com', recipients=[recipient_email])
      msg.body = message
      mail.send(msg)
  
output:     msg = Message(subject, sender='example@example.com', recipients=[recipient_email])
      msg.body = f"Dear {recipient_name},\n\n{message}"
      mail.send(msg)