Although, that is an old tutorial and has been passed on with these two.
Through SendGrid REST API.
https://www.wix.com/corvid/forum/wix-tips-and-updates/example-send-email-with-the-sendgrid-rest-interface
Through SendGrid NodeJS.
https://www.wix.com/corvid/forum/corvid-tips-and-updates/example-send-email-with-the-sendgrid-npm-interface