How Resend Is Designing Its Email Platform for AI Agents and Developers

Zeno Rocha opens by saying Resend has crossed the number of downloads that SendGrid recorded earlier this year, and that it is now more than double that figure. He says the platform is powering 4.3 million users as of the morning of the recording.

He names Warner Bros. and HBO among Resend's customers, and says a Japanese group recently brought roughly 20,000 domains, which he describes as 20,000 different top-level domains registered with different registrars.

Rocha says he is known more for his recent work than for earlier projects such as the Dracula theme. The host recalls him as an indie hacker whose work had taste, and Rocha says he did not expect to build an email company.

He says he was a front-end developer with no infrastructure background, and that he had used Mailgun, Mailchimp, and SendGrid. He felt the market had many players and many competitors, but none focused on developers.

He describes the question that drove him as what a Stripe for email would look like, and says he started without prior knowledge of email infrastructure.

The host says a coding agent recommended Resend even though he already used Cloudflare's built-in email, and he asks how Resend gets into those recommendations. Rocha says he spends a lot of time on answer engine optimization, and he traces his interest to earlier tools such as Heroku and Netlify, arguing that each generation has its own defining tools and that this generation is not distributed in the same places.

Rocha explains that inbox providers throttle large sends and watch engagement to decide how many messages to deliver. Sending to the most engaged audience first is part of Resend's queue strategy.

He says the pattern of an abuser is the opposite of what a legitimate platform should look like. Abusers buy new domains and send in a single burst, so Resend works in the other direction.

Rocha says open rates are no longer a reliable metric because spam filters now check tracking pixels. Teams therefore rely on click tracking, but click tracking is difficult because the URLs, and the image URLs, have to match the sending domain.

He says abusers use this same pattern by hosting images elsewhere, pointing links elsewhere, and sending from a trusted domain. Resend initially did link rewriting to its own domain, which he says he thought was normal, but he says it creates a noisy neighbor problem.

If one customer using click tracking sends phishing, the shared domain can be blacklisted, and it can take days or weeks to get off the list, which Rocha says leaves the business in trouble.

Rocha says that if support were software, it would be on about its fourth major version. In the first version, he was answering tickets himself and was very stressed, and he wanted anyone who could sit in the chair.

That version did not work because the team needed someone who would prevent tickets from happening in the first place. The second version was a hire with domain expertise who still did not document answers before responding.

The team then adopted a policy that support replies can only contain a link to a knowledge base article. Rocha estimates that answering a ticket this way takes about an hour and a half, but it built the knowledge base. He says Resend went from about 1 million users in December to 4 million, so adding people alone would not solve the problem.

The host says it is hard to start an email company without someone on the inside at a provider such as Gmail. Rocha agrees that the industry relies on relationships and says Resend did not have those relationships at the start.

To fill that gap, Resend hired for key deliverability roles, including people who had been at Postmark from its early days and people who had been at Mailchimp 15 years earlier. The company then used that network to reach mailbox providers.

Rocha says he could not have predicted what AI would do, but he is glad the company chose to be infrastructure as a service rather than software as a service.

The host asks whether the purpose of Twilio's SendGrid acquisition is to turn an email service into a communications platform that reaches users across channels. Rocha says he admires Twilio, which he says invented that developer category, but argues Twilio has neglected the developer base that built it.

The host raises the question of how a company that is much larger can fail to use its size to win, and asks whether scale provides benefits at all. Rocha says SMS and email are commodities, so margins are thin, and he wonders why Twilio bought SendGrid instead of the reverse.

The host mentions a newsletter with about 5 million subscribers that reportedly sends through Amazon SES for about $5,000 a month. Rocha calls SES the low-cost player from a very established provider and says Resend also started on SES.

Resend focused on the developer experience layer, offering SDKs for every language, because he felt that was underserved. He says the hidden cost of SES is that you need SNS for events such as bounces, complaints, opens, and clicks, then CloudWatch for logs, then SQS once volume grows, and then webhooks, each adding another piece to build.

Rocha says Resend is now building its own infrastructure, including IP block purchasing, pool management, traffic control per mailbox provider, and provider relationships. He says the motivation is observability: he wants to know whether an email was delivered or landed in promotions.

Rocha says he recently saw an issue in which a call could not put everything on the contacts, and he wondered whether too much data was being sent to the client. He says the concern that too many tools confuse agents was bigger earlier, but he no longer sees it as much and is adding more to the MCP.

He says the MCP launched with roughly 20 tools or fewer and now has 80-something. Getting to full coverage of the dashboard is very difficult, because it involves usage billing, team invites, account provisioning, and deletion, and it is an open question whether each should be exposed as an API.

The host agrees and says Next.js's server components and pages can make it easy to avoid exposing a public API. Rocha says Resend started with its API on Next.js and that the bill was so high they had to change course.

The host says Rocha seems to maximize everything, including every SDK, and asks why he cares about so many. Rocha says he is trying to optimize for users in the margins, including people with poor Wi-Fi and older computers in other countries, as he experienced growing up in Brazil.

He says that is why Resend has a free tier and why it covers many SDKs. Resend builds every SDK by hand, including Java and Rust, rather than using generators such as Stainless or Fern, because the team did not like the generated output.

Rocha acknowledges that only a few hundred of the 4 million users may use a given language and says he cares about those users.

Rocha describes inbound email as the basic abstraction, and says the next step is letting a developer create dozens or 100 inboxes programmatically for a reason. He says that would require APIs for reading messages, marking them as read, starring them, and labeling them.

He says the company will launch a product around this soon, and that it is entirely API-driven. He names Missive, Help Scout, and Front as comparable shared inbox products and offers the host a feature flag.

Rocha says he does not have the exact figures at hand, but the vast majority of email goes to Gmail, at least around 60 percent, with Outlook, Yahoo, and other providers following, and then a long tail of smaller ones. He adds that Apple is also a big player, and that Apple's privacy changes make deliverability to Apple addresses harder, since Apple auto-generates relay addresses and its inboxes are stricter about what gets through. For that reason, Resend has an in-product wizard that helps domain owners register with Apple so their emails can be delivered there.

Rocha describes asking a model to compare email providers for sending 1.2 million emails, and says it gave a completely wrong answer about Resend's pricing. The model also said Resend's pricing was opaque, which Rocha says was not accurate.

He explains that the cause was that agents cannot execute a JavaScript widget on the calculator page. The fix was to create a markdown version of that same page, which he says began receiving a tremendous amount of access. Asking again a few days later produced the correct numbers.

Rocha says markdown page access happens on the server and does not show up in regular analytics, so the team had to use Datadog to track it. He says the cost of this approach is that there is no single source of truth, so the markdown and the page must both be updated.

Asked whether they used SEO or AEO consultants, Rocha says Resend never really did. The host notes that Resend seems to have done everything itself.

Rocha says the state of the field was that most people said to do normal SEO and not block AI chatbots, and that most tools simply tracked mentions and let users run experiments. He says he has an unfair advantage as a content business that publishes constantly, and he notes that Opus 4.5 seems to favor newer tools.

Rocha tells listeners to connect their agents to analytics and codebases so the loop is fully complete, which he calls auto research. He describes a CMO agent that researches ideas, keeps track of what has been tried, and spawns other agents, while Rocha signs off on experiments that run during an experiment window and are monitored by other agents.

He says the loop also needs tools, and he has subscribed to AHFS and Data for SEO and built his own AEO tracker. Rocha says the team tried all the major tracking products and now has four subscriptions, and that Reddit, Hacker News, and Twitter matter less than they used to for recommendations.

Rocha says a partner told him he worries too much about design, and that he would have gotten further if he did not. He says that hurt because it was true, but he decided he would rather build a product with a strong design identity used by 1,000 people than a product with 10,000 users that he does not want to use himself. He separately says he would rather be a company of about 10 million dollars in annual recurring revenue where his daughter wants to play with him than a hundred-million-dollar company where she does not.

He says the email industry had many terrible products without enough design, so he saw design as a differentiator in a crowded market. He links the decision to his daughter, saying he would rather be a company of about 10 million dollars in annual recurring revenue where he plays with his daughter than a company worth a hundred million where she does not want to play with him.

The host says that owning a category is different from creating one. Rocha says Resend calls itself the next-generation SendGrid, or AI-native SendGrid, which he admits is not yet a clear new category.

The host cites HubSpot's inbound marketing as an example of category creation, and says the ideal category is named in two words that need no long explanation, essay, or manifesto. Rocha agrees that this is very hard and says he has seen friends try to do the same.