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Platforms · 2026 · Lead engineer

Email transport & journeys

An SMTP relay on Cloudflare Workers with a hand-written DKIM signer

Private client work: no customer data is shown; the engineering details are mine to share.

Architecture

  • Architecture: platform, Cloudflare Worker with DKIM signer, mail provider

What it is

The cloud host does not offer outbound SMTP, so I built a Worker that speaks SMTP over TLS to the mail provider, signing every message with an RFC 6376 DKIM implementation on WebCrypto. Welcome, first-deposit and catch-up email sequences run on it.

Highlights

  • SPF, DKIM, DMARC, VERP bounces, RFC 8058 one-click unsubscribe
  • mail-tester score 10/10
  • 26 tests