Write an Express server to send email

In this article, I would like to share how to write a Node.js program to send email via Gmail SMTP server using a Google account, and then deploy the program to Google Cloud.

Table of Contents

• Generate App Password
• Write Express.js Program
• Deploy to Google Cloud

Generate App Password

First of all, create App Password to be used in the program. Due to security reason, Google does not allow non Google-app to sign in. It is required to explicitly generate an App Password to use.

In order to generate App Password:

1. Go to your Google Account.
2. Select Security.
3. Under "Signing in to Google," turn on 2-Step Verification.
4. Under "Signing in to Google," select App Passwords.
5. At the bottom,
   • choose "Mail" from "Select app"
   • choose "Other (Custom name)" from "Select device" A textbox will then be shown. Enter meaning description like "Send Email from application".
6. Follow the instructions to enter the App Password. The App Password is the 16-character code in the yellow bar on your device.
7. Tap Done.

Reference: Sign in with App Passwords

Write Express.js Program

• Create package.json.

   {
     "name": "contact-form-server",
     "description": "This script serves as a server to accept and process request from a Contact Form, and then send to data to a destination email",
     "scripts": {
       "start": "node contact_form_server.js"
     },
     "version": "0.0.1",
     "dependencies": {
       "cors": "^2.8.5",
       "express": "^4.17.1",
       "nodemailer": "^6.7.1"
     }
   }

• Create contact_form_server.js (you can have another js script filename, but make sure to change the script name of the "scripts:start" entry in package.json) as the Node.js script.

  • express package is used for running a server.
  • nodemailer package is used for sending email.
  • cors package is used to allow Cross-Origin Resource Sharing.

• Start the program locally for testing.
  
  

   npm start

• Create a HTML form for testing.

Deploy to Google Cloud

• In Google Cloud Console, create App Engine in standard environment using Node.js. The main advantage of running in Standard Environment is that "Application can scale to 0 instances when there is no traffic. Most cost-effective for applications that have significant periods where they are not serving traffic".
• Create app.yaml for Google Cloud deployment.

   runtime: nodejs14

• Enable Cloud Build API. Set the appropriate credential.
• Deploy to Google Cloud.

   gcloud app deploy

• Change the url value in the javascript in HTML form and test.