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.

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