Teamday
← Back

Resend's Zeno Rocha: 80 MCP Tools, Pages Agents Can Read

Latent Space
agentsstartupinterviewbusinessautomation

How Resend's Zeno Rocha Designs an Email API for Agents

Zeno Rocha is the founder and CEO of Resend, the email API company from Y Combinator's Winter 2023 batch. He says Resend now has 4.3 million users, up from 1 million last December, and just crossed 120,000 paid customers, among them Warner Bros. Discovery, HBO and Mistral. On Latent Space the hosts open with the reason they invited him: coding agents keep recommending Resend, even to a host who had already set up Cloudflare email. Rocha explains what he did to get there and what it costs to run a free tier in an industry full of fraud.

Being the default answer was a goal from day one. Resend launched in 2023, a decade behind Twilio SendGrid, Postmark and Mailgun in search rankings, so Rocha wrote short docs for every long-tail combination (not just Python, but Django). When people began asking models instead of Google, he changed the page format: almost every Resend page now ends in an FAQ, the docs and the marketing site publish llms.txt, and every marketing page has a markdown version that agents can fetch by adding .md or through content negotiation. See Answer Engine Optimization.

The pricing page that a model got wrong: Rocha asked a model to compare the cost of sending 1.2 million emails with Resend and its competitors. It got Resend's price badly wrong and called the pricing obscure. The cause was a JavaScript calculator that agents don't operate. He wrote the same numbers out in a markdown version of the page, asked again a few days later and got the right answer. He watches traffic to those pages in Datadog, because normal web analytics never see the requests. "JavaScript widgets they're not going to be executed so I spell out the same data in text"

An MCP server that grew from about 20 tools to more than 80: Resend's first MCP server was an open-source project by Yoko at a16z, one of its investors, which Rocha later asked her to transfer to Resend. Building the hosted remote version meant adding OAuth and reworking the permissions model first. He says calls have at least doubled every month and reached about 1.2 million in August. While Cloudflare exposes two tools, Resend keeps adding them. "Now we have like 80 something tools." His aim is everything the dashboard can do, including the awkward parts like billing, team invites and account deletion. The CLI is growing too, though more slowly than the MCP server.

Official connectors now decide what he buys: Rocha dropped Plausible for PostHog because PostHog maintains its own MCP server and Plausible's was built by a third party. He picks consumer apps the same way. "If it's not there, I don't use it." He wants the product to be "formless": API first, then SDKs written by hand for each language after he rejected generated ones, then CLI and MCP. Customers now tell him they never open the dashboard he spent so long designing.

Trust by default, then block fast: Older email providers make new accounts fill in a form and wait two days for human review. Resend lets everyone in and watches bounce rates, complaint rates and domain signals instead, such as a domain bought two days ago or a website that doesn't respond. One group arrived with about 20,000 domains. "You need to do exactly what an abuser wouldn't do." Rocha says most blocked accounts turn out to be misuse, not abuse. A Mailgun founder had warned him that 90% of that company's R&D went to fighting abusers, which is why Resend automated it.

Support at 4.3 million users: Rocha calls the current setup roughly version four. An early rule did the most to build the knowledge base. "You can only respond to a ticket with a link." If the doc didn't exist, the support person wrote it first, even if that took an hour and a half. Most tickets are still DNS setup, increasingly from users of Lovable, Bolt and v0 who have never seen a CNAME record. Resend adopted Domain Connect, a little-used protocol that works like OAuth for domains, and persuaded Vercel to support it alongside Cloudflare.

6 Takeaways from Zeno Rocha on Building for Agents

  • Write the data out in text - Anything behind a JavaScript widget, such as a pricing calculator or a chart, is invisible to an agent that fetches the page. Resend repeats it in markdown.
  • Ask the models about yourself - Rocha found the pricing error by running his own competitor comparison on a Sunday, then confirmed the fix days later. Resend also pays for four AEO tracking tools, which he says report mentions but don't tell you what to do.
  • Own your MCP server - He treats a vendor-maintained connector in the official directories as a buying criterion, and assumes his customers do the same.
  • Cover the long tail of tools - Rocha no longer sees models getting confused by many tools, so Resend exposes more of the product with each release.
  • Automatic plain text helps deliverability - Resend generates a plain-text version of every HTML email, which Rocha says raised deliverability because spam filters can read it directly.
  • Comparison pages still count - Resend built migration pages with a code converter instead of head-to-head comparisons. Rocha now thinks that was a mistake, because competitors' comparison pages get recommended more.

What Resend's Agent Playbook Means for Software Companies

Rocha's bet is that the buyer's first question now goes to a model, and the model returns one answer where Google returned ten links. Being that answer took plain work: text that agents can read on every page, an official MCP server that covers the whole product, and a free tier with no signup friction. Resend is now building its own sending infrastructure below Amazon SES, has moved its sending path from Node.js to Go and plans an inbox API so agents can read mail as well as send it. For a related view from the documentation side, see Mintlify and Coinbase on docs whose readers are agents.