Local mail without MTA

Goverp · Veteran Joined: 07 Mar 2007 Posts: 1997

This seems to be asked regularly, so my apologies if it's been sufficiently answered before; of course I think it hasn't.

My use case:
Various daemons, such as smartd running on one Gentoo desktop machine, that want to send emails to advise of problems. I use KDE kmail2 for email. I want to get the daemon mail even if my Internet is down.

IIUC, and I think I don't, mailx should be able to do this, all by itself, or at least it should be possible for the daemons to be configured to mail to "admin" userid, without any MTA such as sendmail or postfix. As the mail's not leaving the box, there should be no need for even a thin MTA such as ssmtp. (at the moment I have ssmtp set to route the main to my ISP's SMTP server, which gets the mail to me, but only if the Internet is up. nullmailer may be better, as it appears to queue the mail until the internet comes back, but why should I wait).

Again, IIUC, mailx should put the mail into /var/spool/mail/admin (a.k.a. /var/mail/admin), and that should be configurable as a kmail2 "account" for receiving mail.

However, mailx has a dependency on virtual/mta, so I can't actually configure this. I may be getting confused between mail-mta/sendmail and the sendmail program provided by various MTAs (such as postfix, ssmtp, sendmail), so is there supposed to be a default sendmail program to do local mail, and is it necessary for mailx to operate?

Advanced use case:
As above, but several linux boxes on my local network 192.168.1.0/24 connecting via my router. (Aside: the router has a firewall, and I've no incoming ports open to the outside world (unless it's been hacked).) Would like daemon email to end up in my desktop mailbox, even if my ADSL line is dead but my router is alive.

This version seems to require an MTA, but I really don't need sendmail or postfix, just a simple process to relay the stuff from the source box over the local network to my desktop. The simplest solution may be Gnu mailutils (net-mail/mailutils), which has the advantage of offering maildir support in its clients. It seems to have a lot of USE flags that I'd hope to switch off for this use case (databases, security etc). The mailutils documentation suggests this might not be as simple as I'd hoped. Maybe the other boxes need ssmtp or nullmailer.

The basic trouble is that the use cases are simple, but the common solutions seem way to complex because they address too many irrelevant use cases. I (and I expect others) would be grateful if someone can help me see the wood for the trees.
_________________
Greybeard

khayyam · Posted: Fri Jan 13, 2017 9:49 pm Post subject: Re: Local mail without MTA

cboldt · Veteran Joined: 24 Aug 2005 Posts: 1046

I'll add that I like exim as a lightweight MTA, having used ssmtp and nullmailer for the same function.

szatox · Advocate Joined: 27 Aug 2013 Posts: 3131

Nullmailer doesn't let you receive emails. It's sender-only program.
I've been looking for some agent that would let me receive emails from my daemons too. I tried some tricks with nullmailer etc, and then I trashed it all and installed postfix. Being local-only is irrelevant. Nothing forces you to announce your email server and expose it. You can just as well keep it private, behind firewall, or bound to 127.0.0.1

Goverp · Veteran Joined: 07 Mar 2007 Posts: 1997

Thanks for the explanations guys. I'll have to either install one of the real MTAs, or write my own.

I've realized there's a problem with MTAs restricted to the local network (in my case three boxes, a couple of desktops and a netbook attached to a router); both the MTA and the sender or recipient need to be on at the same time, and I normally only use one of the boxes at a time.

So what I want is an MTA in my router. Which is interesting, 'cos I was thinking of cobbling something thin together with scripts and FTP to move files from maildir to maildir; and my router can run an FTP service. Or maybe I just go back to nullmailer/ssmtp and send everything to my mailbox on my ISP's email system.
_________________
Greybeard

cwr · Veteran Joined: 17 Dec 2005 Posts: 1969

Again for exim - it seems the best compromise for a local MTA.

Wlll

cboldt · Veteran Joined: 24 Aug 2005 Posts: 1046

If you run an MTA (other than ssmpt or nullmailer), it will hold mail that it can't deliver. This happens to me when I take the laptop on the road. When I get back to my LAN, it is not unusual for the laptop to have accumulated a queue of undeliverable mail relating to system cronjobs.

Just saying, after you set things up correctly, it won't matter if the receiving machine is up or down (my laptop away is like my mail server on the LAN being down), the emails will be sent eventually.

Ji.M · n00b Joined: 15 Jan 2017 Posts: 2

how about using 'procmail -d?

dmpogo · Advocate Joined: 02 Sep 2004 Posts: 3267 Location: Canada

Among MTA's that satisfy virtual/mta on Gentoo, there is esmtp. It is no longer maintained, however it has an option force_mda, which make it essentially a local to one machine email service.
Every mail send anywhere is delivered to the local MDA, such as procmail.

That does not solve your extended problem of local network, but should solve the need for mail services getting emails from daemons locally on one computer

ian.au · Guru Joined: 07 Apr 2011 Posts: 591 Location: Australia

dmpogo · Advocate Joined: 02 Sep 2004 Posts: 3267 Location: Canada

Goverp · Veteran Joined: 07 Mar 2007 Posts: 1997

FWIW, I went with opensmtp. It's reasonably lightweight and easy to configure. I put one MTA on each box, and checked I could send mail round the network.
_________________
Greybeard

Zucca · Posted: Fri Dec 23, 2022 8:06 pm Post subject:

I would like to set up something like this, but I've never installed anything more than some smtp command line mail sender. That alone requires receiving mail server.

Then there's MDA which stands for Mail Delivery Agent?
And MTA? Mail Transfer Agent?

Oh well. Until I start up my new home server...
_________________
..: Zucca :..
Gentoo IRC channels reside on Libera.Chat.
--

pjp · Administrator Joined: 16 Apr 2002 Posts: 20067

Mail processing model
_________________
Quis separabit? Quo animo?

dmpogo · Advocate Joined: 02 Sep 2004 Posts: 3267 Location: Canada

Princess Nell · l33t Joined: 15 Apr 2005 Posts: 916

I used to use nullmailer, but recently completely revamped my mutt setup because I found the builtin smtp quite slow. Replaced nullmailer with msmtp. While I'm quite familiar with postfix, I found it overkill for my purposes. msmtp does everything I need, it sends email for various addresses to the resp. providers' SMTP submission host, delivers root's cron email locally and also has a sendmail mode. A very nice feature is the "passwordeval" config option that allows you to have all your passwords (for SMTP) in encrypted files; if you use gpg, you can benefit from gpg-agent.

https://marlam.de/msmtp/