Skip to main content

Sending Emails with Curl: A Nifty Systemd Workaround

I recently tried to create a simple systemd service to send an email notification, but my initial approach with mail and sendmail failed with a strange permission error.

My original service file looked like this:

[Service]
ExecStart=mail --subject=Subject recipient@example.com

The error message was a bit of a head-scratcher: warning: mail_queue_enter: create file maildrop/....: Permission denied.

A quick search pointed me to the cause: the postdrop binary has setgid. However, the systemd setting NoNewPrivileges=true prevents this.

While I hadn't explicitly used that setting, I was using DynamicUser=true, which implies and enforces NoNewPrivileges=true. This meant my service, running as a temporary user, couldn't get the permissions it needed to interact with the mail queue. Note that this implication cannot be disabled/overriden.

I wanted to avoid creating a new, dedicated user for this task. I realized that the problem was how mail and sendmail directly interact with the mail queue. The solution was to bypass that entire process and talk directly to the local SMTP server.

I didn't want to install another dedicated SMTP client. Fortunately, I learned that the curl can also act as an SMTP client! This command worked perfectly, sending the email by directly:

curl --url smtp://localhost:25 --mail-rcpt recipient@example.com --upload-file body.txt
Labels:

Comments

Post a Comment

Popular posts from this blog

Determine Perspective Lines With Off-page Vanishing Point

In perspective drawing, a vanishing point represents a group of parallel lines, in other words, a direction. For any point on the paper, if we want a line towards the same direction (in the 3d space), we simply draw a line through it and the vanishing point. But sometimes the vanishing point is too far away, such that it is outside the paper/canvas. In this example, we have a point P and two perspective lines L1 and L2. The vanishing point VP is naturally the intersection of L1 and L2. The task is to draw a line through P and VP, without having VP on the paper. I am aware of a few traditional solutions: 1. Use extra pieces of paper such that we can extend L1 and L2 until we see VP. 2. Draw everything in a smaller scale, such that we can see both P and VP on the paper. Draw the line and scale everything back. 3. Draw a perspective grid using the Brewer Method. #1 and #2 might be quite practical. #3 may not guarantee a solution, unless we can measure distances/p...
3 comments
Read More »

Qubes OS: First Impressions

A few days ago, while browsing security topics online, Qubes OS surfaced—whether via YouTube recommendations or search results, I can't recall precisely. Intrigued by its unique approach to security through compartmentalization, I delved into the documentation and watched some demos. My interest was piqued enough that I felt compelled to install it and give it a try firsthand. My overall first impression of Qubes OS is highly positive. Had I discovered it earlier, I might have reconsidered starting my hardware password manager project. Conceptually, Qubes OS is not much different from running a bunch of virtual machines simultaneously. However, its brilliance lies in the seamless desktop integration and the well-designed template system, making it far more user-friendly than a manual VM setup. I was particularly impressed by the concept of disposable VMs for temporary tasks and the clear separation of critical functions like networking (sys-net) and USB handling (sys-usb) into the...
Post a Comment
Read More »

Exploring Immutable Distros and Declarative Management

My current server setup, based on Debian Stable and Docker, has served me reliably for years. It's stable, familiar, and gets the job done. However, an intriguing article I revisited recently about Fedora CoreOS, rpm-ostree, and OSTree native containers sparked my curiosity and sent me down a rabbit hole exploring alternative approaches to system management. Could there be a better way? Core Goals & Requirements Before diving into new technologies, I wanted to define what "better" means for my use case: The base operating system must update automatically and reliably. Hosted services (applications) should be updatable either automatically or manually, depending on the service. Configuration and data files need to be easy to modify, and crucially, automatically tracked and backed up. Current Setup: Debian Stable + Docker My current infrastructure consists of several servers, all running Debian Stable. System Updates are andled automatically via unattended-upgrades. Se...
Post a Comment
Read More »