I found that the smtp configuration in the app server is somehow troublesome and sending email using rest api is quite straightforward.
- Get a domain
- Set up a free Business Email with https://www.zoho.com/
- Set up a free account https://www.mailjet.com/ (200 emails a day) (super helpful customer service)
- Install mailjet_rest in the VPS https://pypi.org/project/mailjet-rest/ (the package is installed in the anvil platform for testing as well, thanks Ian for speedy help)
- Detailed code: https://dev.mailjet.com/email/guides/template-api/
Individual plan is required for full Python 3, the emails sent may go into spam