Resend

Resend showed up in 2022, founded by Zeno Rocha, a developer who'd previously worked on open source projects and had a track record of making unglamorous developer tools feel considered. The company went through Y Combinator and built its reputation less on marketing and more on shipping React Email, an open source library for writing email templates as React components instead of hand-coded HTML tables, which is still miserable to write no matter how many years pass. That library predates the paid product and remains free and open source on its own.

The sending API is a non-AI product, and fairly conventional under the hood: SDKs for the usual languages, a dashboard with real delivery logs, webhook support, domain verification that doesn't require digging through six pages of DNS instructions. What made it catch on inside the Next.js and Vercel crowd specifically is that it feels like it was built by people who'd actually been frustrated setting up transactional email themselves, rather than a sales team's idea of what developers want. It's newer than everything else on this list, so it hasn't been tested at the kind of scale SendGrid or Mailgun have over fifteen years, but for a small or mid-size app it's become the default recommendation in a lot of startup Slack channels.