Send Abandoned Cart Reminders with SendGrid

Made by Twilio

Watches a cart collection keeping track of the last updated time of a cart object. When it is over a certain period, send the user an email based on a SendGrid Dynamic Template.

Works with
Cloud Firestore and Authentication
0.1.4 | Source code

How this extension works

Use this extension to automate sending an email reminder to users about items they left in their shopping cart.

This extension will watch the documents added to a specified Cloud Firestore collection. For each document the extension records the last updated time of the document. Then, when the last updated time goes beyond a configurable threshold, the information in the document is copied to a new collection which triggers an email using the Twilio SendGrid API. The information in the document is sent as the template data for a dynamic transactional email.

Additional setup

Before installing this extension, make sure:

Firestore indexes

This extension requires a composite Firestore index. You can add the index in the Firebase console or by the command line.

Indexes in the Firebase console
  1. Go to the Cloud Firestore section of the Firebase console
  2. Go to the Indexes tab and click Add Index
  3. Enter the collection name for your cart collection
  4. Add the following fields to the index:
    • metadata.emailSent - Ascending
    • metadata.error - Ascending
    • metadata.lastUpdated - Ascending
  5. Set the Query scopes to Collection
  6. Click Create
Indexes with the Firebase CLI
  1. In your Firebase project, open your index configuration file, with default filename firestore.indexes.json

  2. Add the following object to the indexes array:

      "collectionGroup": "cart",
      "queryScope": "COLLECTION",
      "fields": [
        { "fieldPath": "metadata.emailSent", "order": "ASCENDING" },
        { "fieldPath": "metadata.error", "order": "ASCENDING" },
        { "fieldPath": "metadata.lastUpdated", "order": "ASCENDING" }

    The collectionGroup name should be the collection name for your cart collection.

  3. Deploy your index configuration with the firebase deploy command. If you only want to deploy indexes, add the --only firestore:indexes flag.

How it works

The shopping cart

A shopping cart should be implemented as a document per cart. How you store items in the document is up to you, but an array property called items containing information about each of the items in the cart is typical. The document should also have a reference to a Firebase Authentication User, either the cart document ID should match the user ID or there should be a userId property on the document. When you create the cart document or update properties on the cart document, the extension will update a metadata.lastUpdated timestamp.

Checking the cart

A function runs periodically to determine whether any carts are abandoned and should be emailed. You can configure the period with the CART_CHECK_INTERVAL using cron.yaml syntax.

There are a few conditions that a cart document must fulfill before it is processed to the next stage:

  • the metadata.lastUpdated timestamp should be older than the configurable ABANDONED_TIMEOUT time in minutes
  • the metadata.emailSent boolean property should be false
  • there should be no errors present in the metadata.error property

If all of these conditions are met, then the extension will attempt to load the user data using the userId property or the document’s ID. If the user doesn’t have an email address, an error will be recorded. If the user has an email address then a document will be created in the EMAIL_COLLECTION. The document will include the user email and a property for dynamicTemplateData consisting of the contents of the user’s cart and a user property including the user’s email and displayName if present. This dynamicTemplateData is used to fill in the fields in a SendGrid dynamic email template.

Sending the email

When a document is added to the EMAIL_COLLECTION the contents are queued up to be emailed using the Twilio SendGrid API. All the information from the cart document is added as dynamic template data for the email. You can configure a DEFAULT_TEMPLATE_ID which is the ID of a SendGrid dynamic template.

You can create dynamic transactional templates in the SendGrid dashboard. SendGrid Templates use Handlebars to render dynamic data into the email.

You also need to configure your DEFAULT_FROM to be an email address that you have verified with SendGrid as either a single sender or via domain authentication. You can also set a DEFAULT_REPLY_TO email.

You can trigger an email to be sent at any time by added a document to the EMAIL_COLLECTION with a to email address and a dynamicTemplateData property.

  to: '',
  dynamicTemplateData: {
    name: "Example"


To install an extension, your project must be on the Blaze (pay as you go) plan

  • You will be charged a small amount (typically around $0.01/month) for the Firebase resources required by this extension (even if it is not used).
  • This extension uses other Firebase and Google Cloud Platform services, which have associated charges if you exceed the service’s free tier:
    • Cloud Firestore
    • Firebase Authentication
    • Cloud Functions (Node.js 10+ runtime. See FAQs)
    • Cloud Secret Manager

Usage of this extension also requires you to have a Twilio SendGrid account and credentials in order to use the Twilio SendGrid API for marketing campaigns. You are responsible for any associated costs with your usage of Twilio SendGrid.