What is the best way to send emails from linux system?

Posted by merpkz@reddit | linuxadmin | View on Reddit | 24 comments

I have configured my homelab internal network with a centralized email server running postfix / dovecot / snappymail combination with virtual mailboxes taken from postgres DB. What I want to achieve is that all other linux servers on my network relays their local destined mails to this centralized box, so that I can read in web interface in the morning that there have been sudoers reported incidents somewhere or some weird cronjob output something on other system. As I understand all I need to do is install MTA, like postfix or sendmail or maybe exim? and create local aliases on that system that emails for root@localhost are actually sent to $me@$internal.domain on my centralized email server. Is it possible to achieve this without installing MTA on every single linux system and just configure them to relay directly to centralized server?

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24 Comments

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rhavenn@reddit

Postfix, sendmail, exim, etc... all would work fine, but overall, they're way to "fat" for what you're trying to do. Look for something more like DMA (DragonFly Mail Agent) or a much simpler MTA that is designed to just listen on localhost:25 / sendmail "binary" call. Alternatively, use a syslog service or a logging agent and something like greylog on your central host. This has the added benefit of being able to add alerting and parsing rules, etc... to your log stream. So, instead of sending email your local services would talk to the local syslog. Since what you mostly seem to be looking for is "centralized logging" doing it via email seems like a "hack" when you have tools available to do "logging". That being said..if it works for you...hack away and have fun / learn something.

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MilkObvious6241@reddit

opa irmao , boa tarde voce teria algum telegram?

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OweH_OweH@reddit

No, that is how a Unix system is supposed to work. I will throw `nullmailer` into the mix here, way way simpler than a full MTA and does exactly what you need: forwarding local system mails to a central relay. I use this on thousands of systems for exactly that purpose.

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Significant_Chef_945@reddit

+1 for nullmailer. We use it on all our Debian/Ubuntu production servers. The config points to our local Postfix server that connects to Sendgrid. Works great!

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merpkz@reddit (OP)

I think this is the answer I was looking for. Just MTA which will accept any local email and forward it to my centralized email system where I can organize it in IMAP folders and read in browser. With other MTAs like sendmail/postfix/exim I would also need to fix aliases, because local emails are delivered to local users and I don't need that. Adding to that - other MTAs usually listen on port 25 and act more like daemons, not that I care particularly about that, but still one less thing to run. Thanks for mentioning nullmailer, will create ansible playbook to configure it on my systems if there are no postfix on system running.

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OweH_OweH@reddit

If you need SMTP on 25 on localhost, then there is also `msmtp`, because `nullmailer` only provides injection via command line. For most things this is more than sufficient, but sometimes programs want to talk via TCP/IP to a mailsystem. Of course you could point those programs directly at your relay server, but in my experience, these programs also do not cope with the relay not being available. So the only real solution is having a relay on ::1 for them to talk to, that then queues and sends the mail off.

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sussybaka010303@reddit

I'd simply write a Python script. Python comes installed by default in most of the distributions and the libraries like \`smtplib\` are preinstalled.

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Moocha@reddit

> Is it possible to achieve this without installing MTA on every single linux system No. To transport mail, you need a MTA. Alternatively, you would need to somehow configure _every single piece of software which wants to send mail_ to behave as a SMTP client and deliver to your central MTA -- which is obviously silly, since most of them don't _have_ a SMTP client built in because it's not their job to deliver mail, that's what the MTA is for :) But if you don't want to use a full-blown MTA, you _can_ make life simpler for yourself and use a lightweight deliver-only MTA emulating the /usr/sbin/sendmail interface such as [msmtp](https://marlam.de/msmtp/) (preferred) or ssmtp (this is still packaged by most distros, but is unmaintained, I emphatically recommend using msmtp instead.)

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TheFluffiestRedditor@reddit

As a longterm postfix user, I install that on my boxes and configure them with a smarthost. That gives me only one mail utility that I have to remember how to interact with, and two defined configurations (SMTP client & smarthost/relay). How does msmtp compare to postfix for ease of use, configuration simplicity, etc? Is there significant benefit from an Admin' perspective?

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Moocha@reddit

Oh, I always use postfix as well. But OP sounded like they weren't all that familiar with it, and msmtp's configuration is arguably simpler due to its much smaller scope (although the distro's postfix config usually already does the heavy lifting anyway, but, alas...) https://wiki.archlinux.org/title/msmtp has a decent overview of what would be required as the base config. /u/oweh_oweh recommended `nullmailer` too; haven't used that one, and it does look to be much simpler based on https://wiki.archlinux.org/title/nullmailer , but it doesn't seem to support OAuth2 which could be a dealbreaker if wanting to relay through one of the big providers.

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OweH_OweH@reddit

Yes, `nullmailer` is not designed for external mail providers to relay through, it is more for relaying through your own infrastructure as a first hop and from there on to external servers. But the advantage is, it really reduces the potential attack surface by being totally simple.

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prairievoice@reddit

I use nullmailer with mailgun, works great

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TheFluffiestRedditor@reddit

Gotcha. I do like Debian's "how would you like to configure postfix today" option, and the generated config file is reasonably sane. I was looking to see if there was something new and useful to add to my list of tools. Looks like I'll be sticking with my tried a true swiss army knife of MTAs \^\_\^ OP's running a homelab, so I hope they haven't yet hit the joy of having to configure OAUTH or SAML.

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What is the best way to send emails from linux system?

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24 Comments

rhavenn@reddit

MilkObvious6241@reddit

OweH_OweH@reddit

Significant_Chef_945@reddit

merpkz@reddit (OP)

OweH_OweH@reddit

sussybaka010303@reddit

Moocha@reddit

TheFluffiestRedditor@reddit

Moocha@reddit

OweH_OweH@reddit

prairievoice@reddit

TheFluffiestRedditor@reddit

Moocha@reddit

bobj33@reddit

sarkyscouser@reddit

neuthral@reddit

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