I have a Linux (Ubuntu) desktop workstation. I would like to be able to send messages to the DC server (which is also the mail server) from a shell script to e.g. notify of a backup completed or such-like, but I really don't want to configure a sendmail server or any other MTA on this workstation. It there a way to send an email without an MTA? I know I could pipe a message into `telnet host 25`, but that seems a bit crude.

Mailx is one solution, but honestly if you've already got a mail server, you don't have to configure really ANYTHING on postfix or sendmail. Just a single line, defining the smart/relay host, and start the service. Any mail will be relayed to the smart host to deal with.
For sendmail, modify the line in sendmail.cf, look for the line that starts with a capital DS, typically blank on new installations:
Postfix, in main.cf
Start either service, and you're done.

So, I guess the answer is "no, you need an MTA". Yes, setting up sendmail is pretty easy, I've done it a-plenty on many systems. I was just hoping to avoid starting another service on this workstation -- and a rarely used one at that.

And, it's not quite true that I "don't have to configure really ANYTHING." I had to get the packages:

apt-get install sendmail heirloom-mailx

and add the following lines to as-shipped /etc/sendmail.mc to make it do what I want:

define(`confDOUBLE_BOUNCE_ADDRESS',`nobody')dnl
define(`SMART_HOST',`my.smart.host')dnl
FEATURE(`always_add_domain')dnl
MASQUERADE_AS(`mydom.org')
FEATURE(`masquerade_envelope')
FEATURE(`masquerade_entire_domain')
EXPOSED_USER(`root')dnl
LOCAL_DOMAIN(`localhost.localdomain')dnl

Then create a new sendmail.cf

service sendmail stop
m4 sendmail.mc >senmail.cf
service sendmail start

Not A LOT of work; so I went ahead and configured sendmail and it works just fine.

THX

Well, mailx will work in this scenario...I only mentioned postfix/sendmail, because (given your environment), you'd only have to set the one line, and it would be lightweight, given it's only sending the occasional email out.
Glad it's working for you.

Oh wait! I get it! I could just use mailx and have e.g.

set smtp=my.smart.host

in my $HOME/.mailrc file, and not have sendmail running at all, right? I never tried that before, but I did just now and it seemed to work.

Or I suppose I could use `mailx -S smtp=my.smart.host` - that also works. I didn't realize that's what you guys were driving at.

These ideas are actually better because I don't expect message to be received at this workstation.

Yeah, either will work fine. Mailx has a 'built-in' MTA, to let it talk directly to a smart host for relaying. Personally, just configuring the smart host in sendmail/postfix is my preferred solution, but that's just preference.