Why Nodemailer Doesn't Work on Cloudflare Workers (And What To Do Instead)

A short explanation of a wall a lot of developers hit, why it isn't going away, and the five lines that replace it. You wrote a contact form. It worked locally. You deployed it to a Cloudflare Worker, or a Vercel Edge Function, or Deno Deploy, and got something like this: TypeError: Class extends value #<Object> is not a constructor or null Or, if you were luckier and got a useful error: Module not found: Can't resolve 'net' Then you spent an hour trying compatibility flags, polyfills, and bundler aliases. I want to save you the rest of that hour. This isn't a bug, and no amount of configuration will fix it. The actual reason Nodemailer's default transport is SMTP. SMTP is a protocol that runs over a raw TCP connection. To open one in Node.js, you call net.createConnection() . Cloudflare Workers don't run on Node.js. They run on V8 isolates — the same engine as Chrome, without the Node runtime around it. Vercel's Edge Runtime and Deno Deploy are built on similar principles. In that environment, there is no net module, because there are no raw TCP sockets. All networking is handled by managed infrastructure outside the runtime — Cloudflare's own writeup on bringing node:http to Workers is explicit about this: connection pooling, TLS negotiation, and egress IP management are handled at the system level, which is precisely why a subset of Node APIs can never be supported. So the chain is: No raw TCP → no net.createConnection() → no SMTP client → no Nodemailer. There's a second, smaller issue that often gets conflated with this one. Nodemailer issue #1621 points out that Nodemailer imports built-in modules without the node: prefix, which breaks the Workers build step. That one is fixable. But fixing it wouldn't help — you'd just move the failure from build time to runtime, where net still doesn't exist. Issue #1623 covers the broader edge-function problem. It's worth being clear that none of this is a knock on Nodemailer. It's an excellent library, actively maintained,