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Send Confirmation Emails with Cloud Functions

This sample shows how to send a confirmation emails to users who are subscribing/un-subscribing to a newsletter.

Functions Code

See file functions/index.js for the email sending code.

Sending emails is performed using nodemailer a node based Email client with comprehensive EMail server setup. For simplicity, in this sample we're showing how to send email through SMTP using a Gmail account. Be aware that Gmail has an email sending quota. If you are planning on sending a large number of emails you should use a professional email sending platform such as Sendgrid, Mailjet or Mailgun.

If switching to Sendgrid, Mailjet or Mailgun make sure you enable billing on your Firebase project as this is required to send requests to non-Google services.

The dependencies are listed in functions/package.json.

Sample Database Structure

When a signed-in user subscribes or unsubscribes to the mailing list we change the subscribedToMailingList boolean:

/functions-project-12345
    /users
        /$uid
            subscribedToMailingList: true,
            email: "user@domain.com"

Then the email stored here is used by the function to send the email.

Trigger rules

The function triggers on changes to /users/$uid and exits if there are no changes to subscribedToMailingList.

Setting up the sample

  1. Create a Firebase Project using the Firebase Console.
  2. Enable the Google Provider in the Auth section.
  3. Clone or download this repo and open the email-confirmation directory.
  4. You must have the Firebase CLI installed. If you don't have it install it with npm install -g firebase-tools and then configure it with firebase login.
  5. Configure the CLI locally by using firebase use --add and select your project in the list.
  6. Install dependencies locally by running: cd functions; npm install; cd -
  7. To be able to send emails with your Gmail account: enable access to Less Secure Apps and Display Unlock Captcha. For accounts with 2-step verification enabled Generate an App Password.
  8. Set the gmail.email and gmail.password Google Cloud environment variables to match the email and password of the Gmail account used to send emails (or the app password if your account has 2-step verification enabled). For this use: 
    firebase functions:config:set gmail.email="myusername@gmail.com" gmail.password="secretpassword"

Deploy and test

This sample comes with a web-based UI for testing the function. To test it out:

  1. Deploy your project using firebase deploy
  2. Open the app using firebase open hosting:site, this will open a browser.
  3. Sign in the web app in the browser using Google Sign-In and delete your account using the button on the web app. You should receive email confirmations for each actions.