How does Resend ensure email deliverability for high-volume sending?

Resend employs sophisticated techniques such as queue management, prioritizing engaged users, spacing emails across providers, managing IP blocks, and reverse-engineering abuse patterns to build opposite, secure features. They also focus on domain reputation over IP reputation.

What are the technical challenges in sending mass emails?

Key challenges include respecting the unique rules of different mailbox providers (Gmail, Outlook), avoiding throttling by sending in managed batches, managing IP reputation, and understanding engagement signals like opens and clicks.

Why is plain text email important for deliverability?

Plain text emails are easier for spam filters to parse directly without complex HTML rendering, which can improve deliverability. Resend automatically generates plain text versions from HTML to enhance this.

How does Resend handle potential abuse and spam with its open sign-up policy?

Resend trusts users by default but quickly blocks accounts upon detecting anomalies like high bounce or complaint rates. They differentiate between misuse (skill issue) and intentional abuse, prioritizing rapid intervention.

What is the significance of Domain Connect for email infrastructure?

Domain Connect is a protocol that simplifies DNS configuration, akin to OAuth for domains. It allows service providers like Resend to connect with DNS providers, reducing user friction in setting up email services.

How does Resend approach SEO and getting recommended by AI models?

Resend focuses on detailed documentation, long-tail keywords, and answering user questions directly through FAQs on every page. They also leverage the recency bias of AI models by encouraging organic content creation and discussion about their product.

What are the differences between marketing and transactional email services?

Transactional emails are typically straightforward queue-based messages, while marketing emails involve complex batching, speed analysis, and engagement monitoring. This complexity often leads to different pricing models, with marketing emails sometimes being more expensive due to per-contact charging.

How does Zeno Rocha balance being a founder with being a father?

Zeno prioritizes his family, especially his daughter, over extreme financial success, choosing to live in a reality where he is close to his family even if the company isn't worth hundreds of millions. He focuses on setting priorities and being present.

What is Resend's philosophy on product development and breadth of features?

Resend believes in covering the entire surface area, aiming for an API-first approach and supporting numerous languages and tools. This strategy, including maximizing SDKs and MCP integrations, is partly driven by optimizing for users with limited resources.

How does Resend view the future of email communication?

Resend sees email moving from single-player to multiplayer modes, with collaborative editors and programmatic access to inboxes. They are also developing inbound email capabilities to facilitate programmatic inbox creation and management.

What is the significance of building custom infrastructure vs. using cloud providers like AWS SES?

While cloud providers offer ease of use, building custom infrastructure allows for greater control, better performance, and potentially lower costs by avoiding the complex 'apparatus' of services like SNS and CloudWatch needed to supplement AWS SES.

Key Moments

Designing for Agents — Zeno Rocha, Resend

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Key Moments

TL;DR

Resend's co-founder reveals AI models like Claude Code recommend Resend for email services, but scaling infrastructure and battling abuse are the real challenges behind its rapid growth.

Key Insights

Resend now powers 4.3 million users and has surpassed SendGrid in SDK downloads, indicating significant adoption.

Despite its rapid growth, Resend started with no prior knowledge of email infrastructure, focusing on developer experience.

The complexity of email deliverability involves intricate systems to manage IP reputation, batching, and provider-specific rules for services like Gmail and Outlook.

Resend's philosophy trusts users by default but aggressively blocks abuse at the first sign of trouble, a departure from traditional email service providers' strict onboarding.

The company manually generated all its SDKs in different languages (Java, Rust, etc.) to ensure the best possible developer experience for each.

While Resend offers a free tier to encourage adoption, it faces significant abuse, especially from entities registering thousands of domains for illicit purposes.

From Indie Hacker to Email Infrastructure Leader

Zeno Rocha, co-founder and CEO of Resend, shares his journey from creating popular VS Code themes and being an indie hacker to building a major email infrastructure platform. He initially felt that existing email service providers like Mailgun, Mailchimp, and SendGrid underserved the developer persona. This observation led him to build Resend with the premise of creating the 'Stripe of email,' focusing on a seamless developer experience. Despite knowing nothing about email infrastructure initially, the company has achieved significant milestones, now powering 4.3 million users and exceeding SendGrid in SDK downloads.

The complex art and science of email deliverability

Sending emails at scale, especially to major providers like Gmail and Outlook, is far more complex than typical application scaling. It involves respecting intricate rules set by each email provider, which differ significantly. For instance, sending a large volume of emails requires careful batching and sequencing, prioritizing more engaged recipients first to avoid throttling. Resend also manages IP reputation by purchasing and distributing IP blocks across different pools, balancing them over time. This infrastructure game is a constant balance of automation and strategic decision-making to ensure emails reach the inbox rather than spam folders. The goal is to mimic legitimate sending patterns, which are the opposite of how abusers operate.

Resend's philosophy: Trust by default, rapid intervention for abuse

A key differentiator for Resend is its trust-based onboarding. Unlike many traditional providers that require extensive verification and often deny access, Resend allows users to start immediately. However, this trust is coupled with aggressive monitoring. The moment an anomaly is detected through bounce rates, complaint rates, or feedback from mailbox providers, Resend acts swiftly to block the user. This approach aims to avoid penalizing the entire user base for the actions of a few bad actors, a philosophy Zeno Rocha calls 'born free.' This contrasts with a 'prison first' mentality where users must prove themselves before gaining full access. The company has developed sophisticated internal systems to combat the pervasive fraud, phishing, and abuse in the email industry.

Automating support and scaling with a developer-first mindset

Scaling support has been a significant challenge for Resend. They've iterated through multiple support versions, from simple ticket answering to requiring support staff to create knowledge base articles for every response. This process, though time-consuming, built a robust documentation base. Even with growth, the company emphasizes that throwing people at the problem isn't sustainable. They aim to embed best practices directly into the product, reducing the need for manual support. A major pain point for new users is DNS configuration, which Resend is addressing through initiatives like 'Domain Connect,' an OAuth-like protocol for domains that simplifies setup by allowing users to connect their DNS providers directly.

Innovating beyond traditional email services

Resend isn't just focused on sending emails; they are building out a comprehensive developer experience. This includes features like automatically generating plain text versions of HTML emails to improve deliverability, which helps spam filters parse content more easily. They also address the limitations of open tracking (which is becoming unreliable due to privacy changes like Apple's) by emphasizing reliable click tracking and ensuring tracking URLs match the sending domain to avoid blacklisting. The company is also investing heavily in inbound email capabilities, allowing developers to programmatically create and manage inboxes, read emails, and apply labels, aiming to abstract the complexity of email reception.

Strategic product expansion and AI integration

Resend's product surface area is expansive, driven by a philosophy of 'maxing everywhere.' They offer SDKs in numerous languages, generated manually for optimal performance, and provide tools like a CLI and an API-first approach for maximum flexibility. The growth of their Message Composition Protocol (MCP) is particularly notable, with significant month-over-month increases, indicating strong adoption by AI agents and developers working in cloud IDEs. This strategic decision to build out a broad ecosystem, including custom integrations and tools like the CLI for job applications, caters to a wide range of user needs and preferences, optimizing for user experience across different platforms and skill levels.

The evolution of email and the future of communication channels

The conversation highlights the evolving landscape of digital communication. While email remains central, channels like SMS and WhatsApp are also gaining prominence. Resend sees potential in these areas and plans to expand. The company is also looking closely at how AI agents will interact with email, seeing it as a natural extension of their mission to simplify developer workflows. The introduction of inbound email APIs is a step towards enabling agents to process and act upon email content programmatically, further abstracting complexity for developers and creating new possibilities for automated communication.

Balancing ambition with personal priorities

Zeno Rocha emphasizes the importance of balancing intense ambition with personal life, particularly as a father. He shares a story about prioritizing his daughter's well-being and his desire for a close relationship over pure company valuation. This philosophy influences his approach to building Resend, focusing on product identity and developer experience, even if it means slower growth compared to some competitors. He advocates for founders to define their own priorities, whether it's family, design, or specific technological advancements, rather than solely chasing external metrics. This personal reflection underscores a broader theme of sustainable growth and meaningful impact over sheer scale.

Mentioned in This Episode

●Software & Apps

●Companies

●Organizations

●People Referenced

Resend's Email Sending Best Practices

Practical takeaways from this episode

Do This

Respect email provider rules (Gmail, Outlook, Yahoo).

Segment your audience and send engaged users first.

Space out email batches across providers.

Manage IP pools and balance them over time.

Send consistently, avoiding large sporadic bursts.

Reverse-engineer phishing tactics to build opposite features.

Bake best practices into the product, like autogenerating plain text versions.

Rely on click tracking over open tracking, ensuring URLs match sending domains.

Trust users by default, but block quickly upon noticing anomalies.

Focus on developer experience (DX) with comprehensive SDKs and guides.

Use subdomains to segregate email reputation (e.g., transactional vs. marketing).

Consider .com TLDs for improved deliverability.

Focus on documentation (docs) for SEO and user guidance.

Leverage AI agents for content generation and SEO analysis.

Optimize for performance and choose appropriate languages (e.g., Go for sending path).

Make products API-first to cover diverse use cases.

Ensure official, vendor-maintained MCPs for AI integrations.

Optimize for users with limited resources (terrible Wi-Fi, older computers).

Build for multiplayer collaboration in email creation.

Provide both UI-based and programmatic access to features.

Consider inbound email capabilities for programmatic inbox creation.

Ensure domain reputation is managed, not just IP reputation.

Track mentions and get organic content about your product.

Offer frictionless sign-up (free tier, unauthenticated usage).

Avoid This

Don't assume email sending is simple; it requires infrastructure expertise.

Don't rely solely on open rates for deliverability tracking.

Don't rewrite link tracking URLs to your own domain if it risks shared blacklisting.

Don't use lookalike domains that mimic legitimate ones, as it appears like phishing.

Don't ignore the hidden costs and complexity of AWS SES.

Don't neglect the developer experience (DX) layer.

Don't rely on unofficial MCP integrations; seek vendor-maintained ones.

Don't block AI chatbots from crawling your site.

Don't neglect comparison pages and migration tools for SEO.

Don't forget that enterprise customers have different needs than standard users.

Don't let the business model of contact-based pricing break your service.

Don't neglect the importance of family and personal life for entrepreneurial ambition.

Don't focus solely on outbound marketing; consider category creation.

Don't assume old SEO tactics will work with AI-driven search.

Common Questions

Resend is an email infrastructure platform founded on the principle that existing solutions overlooked the developer persona. It aims to be the 'Stripe of email,' simplifying sending and managing emails with a focus on developer experience and modern infrastructure.

Topics

Ai Agents Technology & Innovation Programming & Software Business & Entrepreneurship Product Strategy Startup Growth Developer Experience Cloud Infrastructure Email Infrastructure

Mentioned in this video

Companies

SendGrid

An email sending service that Resend has surpassed in downloads. It was acquired by Twilio.

OpenAI

Mentioned humorously in the context of bribing for Resend's inclusion in Cloudflare's recommendations.

HBO

A customer of Resend.

Moz

An older SEO tool provider known for more opinionated advice compared to current AI-focused tools.

Amazon

Amazon Simple Notification Service, required as part of the apparatus when using AWS SES for event feedback.

Coca-Cola

Mentioned as an example of a large company whose brand could be mimicked by fishing domains.

Profound

An AI SEO tool that Resend uses for tracking mentions and experiments.

HubSpot

A company that successfully created the category of inbound marketing, used as an example of category creation.

Stripe

A payment processing company that Resend aims to emulate as the 'Stripe of email' for its developer-centric approach.

Mailgun

An email sending service that Resend's founder used and considered when developing Resend.

Zix

A webhooks-as-a-service company mentioned in the context of difficult category creation.

Netlify

A web development platform, mentioned in the context of the evolution of developer tools.

Postmark

An email infrastructure provider that has exited, mentioned as a competitor and a source of experienced hires for Resend.

Cloudflare

A company that offers built-in email services and recommends Resend, highlighting Resend's integration and adoption.

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