Joe Petrich

Product solutions engineer @google-pay, Pitt CS grad, ham radio enthusiast, linguist

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A simple email signup and verification service using Google Cloud Functions

Published Feb 21, 2021

As I’ve been working on this website and considering what to share on it, I remembered the advice of a friend of mine, Zak, in an article he wrote called How to Stay In Touch With Your Network. In it, he recommends having a personal website and an email list to use when sharing a personal newsletter. I’ve been reluctant to start sending out a newsletter as I can’t share most of my work at Google, but I have enjoyed writing here on my own website, and I decided to build an email list to share the thoughts and projects I put here. As a software engineer, I thought it would be fun to build my own email signup and verification service instead of using one of the many free or paid options. This post explains how I did it. If you want to jump straight to the code, you can check it out on my GitHub here.

Choosing an architecture

I wanted to build an email signup service that I wouldn’t have to think about after deploying it. If, for some reason, my email list grows to the point where I need to worry about scaling I’ll likely migrate to another solution, so I decided to focus on something that would be quick to spin up and scale out to dozens or hundreds of emails easily. Given these requirements, I ruled out hosting my own server, which would require monitoring and consistent maintenance. I’ve used Google App Engine, and that was my first thought, but then I remembered the simplicity of AWS Lambda, which lets you run simple functions in a variety of languages without worrying about even the serving framework. I decided to see if Google Cloud has a similar offering since I don’t have a personal AWS account, and I found Cloud Functions. Similar to App Engine, Cloud Functions allows using a variety of languages. I chose Node.js because it’s quick to prototype and I’ve written App Engine apps in Node before.

After picking Cloud Functions for hosting, I needed to figure out how to collect emails, send a verification email, and accept confirmation of receipt of that email. Collecting is easy - host a form here on that POSTs to my Cloud Function. I decided to use Cloud Firestore for my database as it’s easy to get going and has a high free quota. It would have been just as reasonable to create a structured database, but I didn’t want to worry about a schema while building out the prototype. For sending a verification email, I found the nodemailer package which clearly documented how to send emails through Gmail using OAuth2. For receiving confirmation of receipt of the verification email, I decided on a second Cloud Function that would take a URL parameter identifying the user to mark the address as verified. A final feature I haven’t implemented yet is unsubscribe. I plan on building a third Cloud Function that will be accessible through a unique link in each email that a user can click on to remove themselves from my email list.

Email verification

Though this is a toy project, I am using it on my website, and wanted to take reasonable steps to prevent abuse. For this reason, I wanted to make users verify their emails before they’re added to my list, and I wanted this verification to need to be done through an email they receive, so it will be impossible for someone to subscribe email addresses they do not own. To do this, I decided to generate a random and unique string for each email address that subscribes. This string is appended to the verification URL as a query parameter, and the URL is sent in the verification email. The emailVerification Cloud Function checks the verification code against the value in the database and only activates the subscription if the code in the URL matches. I’m only using random numbers from the Math.random package, which does not generate cryptographically sound random numbers, but the code is only used for email subscription, not authentication, so I was happy to make the tradeoff of security for simplicity.

User experience

Since I’m hosting the signup and verification endpoints using Cloud Functions and my website is hosted on GitHub pages, hosting the endpoints on the domain was going to be more difficult than I thought it was worth. Ideally, the endpoints would be at and, which would allow me to call them from frontend JavaScript on my website, and either redirect to a confirmation page or simply change content on the home page in response to the signup request. Since they’re hosted on different domains, the POST request is done through specifying the action on the HTML form element itself, so I redirect the user to a “thank you” page by returning a redirect status code in the response from the Cloud Function. This works to make the user experience what I want it to be, but limits my flexibility in the future. I’ll probably switch to hosting these endpoints on pretty soon.

Final thoughts

What did you think of this article? What could I have improved in building out this email subscription service? Let me know by sending me an email at If you’d like to receive future posts via email, you can sign up using the service described here by entering your email address in the form underneath my picture.