Scaling Email Infrastructure: Resend's Success with Svix Webhooks

Resend is an email platform for developers. You can think of it as the Stripe of email.

Resend is currently used by more than 150,000 companies and developers to power their email. They have been helping companies of all sizes from Warner Brothers to Anghami (Spotify of the middle east), all the way to small stratups that are just getting started and indie hackers.

As a Y Combinator company themselves, they also target YC companies; seeing traction close to other YC standouts such as Supabase and PostHog.

We started by offering an API, and very quickly, much more quickly than I thought, people were bringing up webhooks all the time. They all said it's great that we have an API, but what about webhooks?

Webhooks are complex, but they are also table-stakes

When Resend started they already knew they were going to be developer and API first. They first built the API, and very quickly people were bringing up webhooks all the time.

They knew this feedback was important, as there are many use-cases that are only made possible using webhooks. For example, when someone marks an email as spam, you may want to remove them from a mailing list. Or when an important emails fails delivery, you want to take action on it.

At my previous company (WorkOS) we had to build a lot of infrastructure internally to support webhooks. It was very complex, hard to maintain, so when I started Resend I already knew we didn't want to build webhooks ourselves.

They wanted to offer webhooks to their customers, but Zeno knew first-hand from his time as the VP of Developer Experience at WorkOS, that building webhooks involves a lot of upfront work, maintenance, and complexity. They wanted to focus on their core business, sending emails, and not on all of this adjacent infrastructure.

They knew they had to launch webhooks, but they also knew they didn't take on all of this additional complexity.

They found Svix, evaluated it, and decided to use it for their webhooks. It was one of the first services they used in the product, incorporating the company in January, and going live with Svix in March the same year.

Or as Zeno put it: Svix saved our lives at that point, because it was a very important piece of what people were pulling us towards, but it's also an area we just couldn't go to at that moment. We needed to focus on sending emails, not webhoooks.

Webhooks make your platform powerful

Resend is API-first, but as Zeno said: API first only gets you halfway there, it essentially means that everything you can do on the dashboard you can do via API. Though your platform is still not programmable, the missing piece is being able to react to events and state changes as they happen. That's why you need webhooks.

Even if you add APIs for every operation on your platform, if you don't know when to call those APIs, your platform is not really programmable. Webhooks are the difference between building a script against your API, and building a tight integration and automated workflows.

Resend started as API first. They are now API and webhooks first. Whenever they are thinking about adding a new feature they first ask themselves: how are the webhooks for this going to look like?

We decided to focus on the what differentiates Resend, and leave the webhook infrastructure to someone that knows how to build and scale webhooks infrastructure.

Resend needed a partner they can scale with

Resend is a fast growing startup. When they launched the company in January 2023 they had 10 users, by March (when they launched webhooks) they had 200 users, but now they already have 150,000. In this time frame they moved from 0 webhooks a year, to more than 200m. It's a completely different scale, and they needed a partner that they can scale with.

They have chosen a variety of different services when they first started the company, but Svix is one of the only ones that they still use to this day. They outgrew many other products, but Svix continued to just work and be a great fit even as they grew.

We just needed something that would scale with us, and I'm really happy for choosing Svix. It's one of the only providers that is still a great fit as our volume and team grew. No downtime, no issues, just reliably working in the background.

Quick implementation, endless customizability

It took Resend a couple of days to build the initial integration, and another week to launch it to their customers. Their initial integration used the Svix consumer application portal. However, being well known for their cohesive user interface, Resend wanted more control over the exact look and feel.

That's where Svix's customizability came into play. They utilized the Svix React libraries to build their own webhook management UI using their own UI components and design language. Making Svix behave and feel exactly like the rest of their product.

Or as Zeno put it: This is great, because my favorite products out there, they solve a problem from different angles. A company like Stripe, Clerk, or Svix in this case, give you both the primitives to take actions, as well as higher level abstraction layers. You can either build things yourself using the API, use a React library with pre-built components, or use a pre-built UI that takes one line of code to integrate.

He then continued: When we first started with Svix we wanted to move as quickly as possible, so we used the app portal. Though when then realized that webhooks are such a core part of our product, that we have to make it feel like our own; which is when we reached for the other abstraction layer, the React libraries.

Webhooks empower your customers

One of the thing that Resend found most powerful about adding webhooks to their product is the countless workflows that people built on their platform that they never expected.

No matter how many customers you speak with, and how great your product is, you can't please everyone. Webhooks empowers your customers to build the workflows that they need on top of your product. Turning a great project, into a core part of your customers' workflows.

That's the beauty, that what makes this whole thing a home run. Even if you build an amazing product, you can't please everyone. That's the magic of building something extensible, you empower people to solve their unique problems.

The end result

Resend built their Svix integration in a bit more than a week, and seamlessly scaled with the platform from 200 users to 150,000. Currently sending over 200m webhooks a year using Svix. Their customers rely on their webhooks, and every time they add a new feature they first think on what webhooks to add for it.

There are many reasons why Resend is loved by developers, but their laser focus on developer experience is certainly one of them.

There is a new generation of developers tools that follow a different premise. They care about docs, they care about extensibility, they care about multiple abstraction layers, and they care about building something that is more than the ordinary. I hope people see Resend as one of these companies building the next generation, and I'm glad we are building the new generation together.