Files
computer-playbook/roles/sys-svc-mail-smtp/README.md
kevinveenbirkenbachandClaude Opus 5 c55f508e05 feat(readme): draw mandatory and disabled service relations
The cosmos generator linked a consumer to its provider only through an
'<role>' in group_names reference or an explicit provides: name. A hard
dependency has neither -- pinning the provider on unconditionally is
exactly what removes the Jinja reference the generator was reading -- so
web-svc-asset's bond to web-svc-file vanished from the diagram the moment
it became binding. Match a service key against the provider's own primary
key from the registry, in both directions.

Services the role turns off drew a solid 1:1 edge, claiming a mandatory
relationship for something that carries nothing at deploy time. They now
render as a red 0..0 edge; edge merging gained a real precedence so a
provider consumed through two keys stays live when only one is off.

Named colour, not hex: a '#' opens an entity code in the mermaid lexer and
turns the whole diagram into a parse error on GitHub.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-08-17 18:02:31 +02:00

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# sys-svc-mail-smtp
## Description
The `sys-svc-mail-smtp` role configures a **local SMTP relay** using [Postfix](https://www.postfix.org/), listening exclusively on `localhost`.
It is designed to be used as a fallback when no central Mailu instance is available, enabling applications and system services to send email via `localhost:25` without additional configuration.
For general background on SMTP, see [SMTP on Wikipedia](https://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocol).
For details about Postfix itself, see [Postfix on Wikipedia](https://en.wikipedia.org/wiki/Postfix_(software)).
## Overview
This role:
- Installs Postfix via `pacman` on Arch Linux.
- Configures it as a **loopback-only relay**, so it:
- only listens on `127.0.0.1`,
- does not perform local mailbox delivery,
- and is safe to use as a simple outbound relay for the local host.
- Integrates seamlessly with the `sys-svc-mail` and `sys-svc-mail-msmtp` roles in the Infinito.Nexus stack.
Typically, `sys-svc-mail` decides whether to:
- Use Mailu (via `sys-svc-mail-msmtp`), **or**
- Fall back to this role (`sys-svc-mail-smtp`) and send via `localhost`.
## Cosmos
The diagram places sys-svc-mail-smtp in the Infinito.Nexus cosmos: the components it deploys (capabilities), the central services it consumes (dependencies), and its outward reach (federation and bridged external networks).
```mermaid
flowchart LR
subgraph role [sys-svc-mail-smtp 💻]
svc_svc_mail_smtp["svc-mail-smtp"]
end
```
Solid `1:1` edges are fixed relationships; dashed `0..1` edges are conditional (enabled only in matching deployments); red `0..0` edges are turned off in this role. Node markers show the role's deploy modes (💻 host, 🐳 compose, 🐝 swarm); ❌ marks a service that is explicitly turned off, and ⚙️ an Ansible role dependency declared in `meta/main.yml`.
## Purpose
The main goals of this role are:
- Provide a **minimal, secure SMTP relay** for hosts that do not run a full mail stack.
- Enable `msmtp` (and any other sendmail-compatible client) to send mail by talking to `localhost:25`.
- Avoid the complexity of a full MTA configuration while still supporting basic outbound notifications.
This is particularly useful for:
- Monitoring nodes,
- Utility hosts,
- Development or test environments without Mailu.
## Features
- 💾 **Postfix Installation on Arch Linux**
- Uses `community.general.pacman` to install the `postfix` package.
- 🔒 **Loopback-Only Configuration**
- Configures `inet_interfaces = loopback-only` to restrict the SMTP daemon to `127.0.0.1`.
- Defines `mynetworks = 127.0.0.0/8` for safe local relaying.
- 🚫 **No Local Mailbox Delivery**
- Sets `local_transport = error: local delivery disabled` to avoid storing mail locally.
- Focus is purely on **relaying** from localhost rather than full MTA behavior.
- 🧩 **Integration with Infinito.Nexus**
- Meant to be driven by `sys-svc-mail`, which decides when to enable this relay.
- Works hand in hand with `sys-svc-mail-msmtp`, which configures msmtp to talk to `localhost:25` when Mailu is not present.
## Further Resources
- SMTP & Mail Transfer:
- SMTP (Wikipedia): <https://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocol>
- Postfix:
- Official site: <https://www.postfix.org/>
- Postfix on Wikipedia: <https://en.wikipedia.org/wiki/Postfix_(software)>
- Related Infinito.Nexus roles:
- `sys-svc-mail`: central mail orchestration
- `sys-svc-mail-msmtp`: msmtp client and sendmail replacement
## Credits
Implemented by **[Kevin Veen-Birkenbach](https://www.veen.world)**.
Part of the [Infinito.Nexus Project](https://s.infinito.nexus/code) and maintained by [Kevin Veen-Birkenbach](https://www.veen.world).
Licensed under the [Infinito.Nexus Community License (Non-Commercial)](https://s.infinito.nexus/license).