# Nullmailer setup

**URL:** https://ps.zoethical.org/t/nullmailer-setup/8727
**Category:** Sysadmin Docs
**Tags:** documentation, howto
**Created:** [January 6, 2025, 7:21pm UTC](https://ps.zoethical.org/t/nullmailer-setup/8727 "2025-01-06T19:21:46Z")
**Posts on this page:** 3
**Page:** 1

<div class="post-metadata">

### Author: ![how](https://ps.zoethical.org/user_avatar/ps.zoethical.org/how/32/2236_2.png) [@how](https://ps.zoethical.org/u/how)
#### Post date: [January 6, 2025, 7:21pm UTC](https://ps.zoethical.org/t/nullmailer-setup/8727/1 "2025-01-06T19:21:46Z")

</div>

By default many GNU/Linux systems run their own local SMTP service on `localhost` to send emails both locally and to the Internet. [Nullmailer](https://untroubled.org/nullmailer/) is a simple SMTP client to send email from a GNU/Linux system to a _smarthost_ (MTA) that will handle the mail delivery. Using a _smarthost_ means the system can send authenticated emails and satisfy modern DNS and email setups. Other options exist, such as [MSMTP](https://marlam.de/msmtp/), or running an MTA like [Exim](https://www.exim.org/) or [Postfix](https://www.postfix.org/), but `nullmailer` offers a most minimalist option.

This document will guide you through installing and configuring `nullmailer` to send administrative email out of a system to the sysadmin group.

## Pre-requisites

1. The domain is configured in [mx.z7l.eu](http://mx.z7l.eu) and in DNS
  - E.g., `host -t mx domain.example` returns `domain.example mail is handled by 10 mx.z7l.eu`

2. The hostname in `/etc/hostname` is a FQDN (e.g., `host.domain.example`)
3. We’re using Debian stable (AKA bookworm at the time of this writing)

## Installation

```auto
apt install nullmailer

```

## Configuration

```auto
cd /etc/nullmailer
# Default destination
x=$(hostname -f); echo "sysadmin.${x//./-}@z7l.eu" > adminaddr
# Default sender (an alias to proc@)
echo "toor@$(hostname -d)" > allmailfrom
# Default domain to append to username
echo $(hostname -d) > defaultdomain
# SMTP credentials (get $PASS from mx.z7l.eu)
install -m 0400 -o mail -g mail /dev/null remotes
echo "mx.z7l.eu smtp --port=465 --ssl --user=proc@$(hostname -d) --pass=$PASS" > remotes
systemctl restart nullmailer

```

## Test

The test email should be simple (single `To:` address, no `Cc:`) otherwise it will create errors that won’t be easy to track.

```auto
cat > ~/test.email <<EOD
Subject: Nullmailer test
From: some.email@domain.example
To: you@ps.zoethics.org

Hop !
EOD
cat ~/test.email | nullmailer-inject boom
journalctl -feu nullmailer

```

Since `allmailfrom` was set, the `From:` address will be overridden. Be sure to replace `you@ps.zoethics.org` by an email address you can read!

## Conclusion

Software on your system will now be able to send notifications to a central email address.

### Caveat

This solution is good for systems with no users except sysadmins, since any user with `sudo` privilege will be able to read the SMTP credentials. But then, systems with untrusted users who can run `sudo` should probably not send email directly.

---

<div class="post-metadata">

### Author: ![natacha](https://ps.zoethical.org/user_avatar/ps.zoethical.org/natacha/32/3145_2.png) [@natacha](https://ps.zoethical.org/u/natacha)
#### Post date: [January 6, 2025, 7:21pm UTC](https://ps.zoethical.org/t/nullmailer-setup/8727/2 "2025-01-06T19:21:46Z")

</div>

hey not sure what this is practically about, I consistantly have issue with smtp, but I am not sure this is about the same thing??

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<div class="post-metadata">

### Author: ![how](https://ps.zoethical.org/user_avatar/ps.zoethical.org/how/32/2236_2.png) [@how](https://ps.zoethical.org/u/how)
#### Post date: [January 6, 2025, 7:21pm UTC](https://ps.zoethical.org/t/nullmailer-setup/8727/3 "2025-01-06T19:21:46Z")

</div>

Nullmailer is for servers, it’s a lightweight way to tie a machine to a single SMTP account for remote (smarthost) email delivery.

A few years ago, it was customary for each server to run its own local SMTP service. But with SPF and DKIM, it became impractical and unsafe to maintain local SMTP service on many machines. Instead, the DNS records a number of machines (“mail exchangers”) that are authorized to send email, and all other machines _must_ use the authorized senders instead of sending email by themselves.