An example of how to perform asynchronous work within a synchronous program, this example using Flask. Code adapted from "Example #1" at https://hackernoon.com/threaded-asynchronous-magic-and-how-to-wield-it-bba9ed602c32

async-send_email-Flask.py

import asyncio
import smtplib
from threading import Thread
from flask import Flask
from email.mime.text import MIMEText

app = Flask(__name__)


def send_notification(sender, recipient, subject, body, server):
    """Generate and send the notification email"""

    # Do some work to get email body
    message = MIMEText(body, 'html')
    message['Subject'] = subject
    message['From'] = sender
    message['To'] = recipient

    # Connect to the server
    server = smtplib.SMTP(server)

    # Send the email
    server.sendmail(sender,
                    recipient,
                    message.as_string())

    server.quit()


def start_email_worker(loop):
    """Switch to new event loop and run forever"""

    asyncio.set_event_loop(loop)
    loop.run_forever()


# Create the new loop and worker thread
worker_loop = asyncio.new_event_loop()
worker = Thread(target=start_email_worker, args=(worker_loop,))

# Start the thread
worker.start()


# Assume a Flask restful interface endpoint
@app.route("/notify/<email>")
def notify(email):
    """Request notification email"""

    worker_loop.call_soon_threadsafe(send_notification,
                                     '{address_from}',
                                     '{address_rcpt}',
                                     '{message_subj}',
                                     '{message_body}',
                                     '{email_server}',
                                     )
    return 'Sent notification to ' + str(email)


if __name__ == '__main__':
    app.run('localhost', port=5000, debug=True)