Mailgun is a great email service with reasonable pricing, including a fantastic free tier. Once you set up the account, sending email from NodeJS is incredibly easy.
Using the node-ses package:
Using MailKit to send email in .NET. The old way with SmtpClient, which was much simpler, is now deprecated in favor of this. For a more thorough example with proper dependency injection and ASP.NET configuration, see this link. View code on GitHub