Is it possible to get the SMTP ports opened on Hetzner?

Yes, you can open a ticket with Hetzner and request an SMTP unblock. It takes 1-2 business days and is not guaranteed. It can be refused on spam prevention grounds. The HTTP API solution is more reliable and can be applied immediately.

How much latency does the Cloudflare Worker proxy add?

No measurable latency. Worker cold start is around 5ms, and the Resend API call is HTTP anyway. The total added latency is lower than an SMTP handshake.

Can I remove the SMTP setting from Listmonk entirely?

No. Listmonk requires at least one SMTP configuration (for validation). A dummy SMTP block has to stay. The actual sending goes through the postback messenger.

Does this solution work with email services other than Resend?

Yes. You can point the code in the Cloudflare Worker at any HTTP API email service (Mailgun, Postmark, Amazon SES API). The Worker only acts as an HTTP bridge.

How much does Listmonk consume?

I started with 256MB RAM and 0.5 CPU, and it runs without trouble. Listmonk is written in Go, a single binary. These resources are enough up to 10K subscribers. The real bottleneck is the database and the email API rate limits.

Listmonk + Resend + Coolify: Sending Email Without SMTP on Hetzner

Hetzner Cloud blocks SMTP ports. The technical detail of how I solved that by running Listmonk on Coolify and bridging to the Resend HTTP API with a Cloudflare Worker postback proxy.

TL;DR

I wanted to run Listmonk on Coolify and send email through Resend. I found out after the install that Hetzner Cloud blocks outbound SMTP ports (25, 465, 587, 2525). Opening a ticket with Hetzner is an option but not a guarantee. As a more portable solution I built a Cloudflare Worker postback proxy. Listmonk sends an HTTP POST to the Worker, the Worker calls the Resend HTTP API. SMTP is bypassed entirely. Stack: Listmonk v6.1.0 + Neon PostgreSQL + Cloudflare Worker + Resend API. Total new components: 1 container + 1 Worker (2.57 KiB).

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