50 lines
1.9 KiB
Markdown
50 lines
1.9 KiB
Markdown
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# tailwart edge — layer-4 mail proxy
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A custom Caddy (with the `caddy-l4` app) that pipes the public mail ports to the
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Stalwart sidecar over the tailnet. Pure TCP pass-through with PROXY protocol —
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Stalwart still terminates all the TLS. **Runs anywhere** with a public IP that's
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on the tailnet and tagged `tag:reverse-proxy`; doesn't need to share a host with
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the mailbox.
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## Why layer 4 and not a normal Caddy vhost
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Web apps reverse-proxy at layer 7 (route by Host/SNI, Caddy terminates TLS).
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Mail can't: port 25 has no SNI (STARTTLS comes after connect), and you want one
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global `:25` listener, not per-domain routing. So the edge is a dumb L4 pipe and
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Stalwart owns the TLS. The novelty you spotted: this is the same `stream`-style
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proxying nginx/Caddy can do for *any* TCP — it just usually isn't used for it.
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## Build & run
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```bash
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docker compose up -d --build # builds Dockerfile (xcaddy + caddy-l4), runs it
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caddy list-modules | grep layer4 # (inside the image) proof the module loaded
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```
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The build fails loudly if `caddy-l4` isn't in the resulting binary.
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## Edit the upstream
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`caddy.json` dials `stalwart.tail7b1641.ts.net:<port>`. If your
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`STALWART_MAGIC_NAME` / `TS_TAILNET` differ, update the five `dial` lines. (JSON
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can't read `.env`; this is the one spot the MagicDNS name is hardcoded — same
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trade-off as pgAdmin's `servers.json`.)
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## The HTTP side (JMAP / autoconfig / admin) is separate
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That part *is* ordinary layer 7. Don't put it here if this box already runs the
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main Caddy on :443 — you'll collide. Instead add a vhost to the existing Caddy:
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```caddyfile
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mail.infinidim.net {
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reverse_proxy stalwart.tail7b1641.ts.net:8080
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}
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```
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## Prerequisites on the host running this
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- Joined to the tailnet, tagged `tag:reverse-proxy` (so the ACL lets it reach
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`tag:stalwart`).
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- Public firewall opens for whichever mail ports you expose (`25` minimum).
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- Nothing else bound to those ports.
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