sys-svc-mail-smtp

Description

The sys-svc-mail-smtp role configures a local SMTP relay using Postfix, 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.
For details about Postfix itself, see Postfix on Wikipedia.

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).

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

Credits

Implemented by Kevin Veen-Birkenbach. Part of the Infinito.Nexus Project and maintained by Kevin Veen-Birkenbach. Licensed under the Infinito.Nexus Community License (Non-Commercial).