SSMTP and a couple similar projects are simplified replacements for behemoths sendmail, postfix or exim. It forwards all the mail it receives to a real SMTP server.

That's exactly what I need--almost. I have one additional requirement. I run cron jobs that send me email. I could tell cron to send email to my external address, but that adds an unnecessary dependency on the internet.

I want to be able to inspect mail sent to the SMTP port. If the 'to' address is of the form "user@example.com", it should be passed on to the external server. But if it's of the form "user@machine", then it's probably from cron (or maybe some other program) and I want it passed to maildrop for delivery on this machine.

So I just need a hook in SSMTP to catch the local stuff.

Is there already such a program anwhere?

That's done by a MTA. As I know it can be done with sendmail, postifx, qmail, exim, openSMTPD software running as daemons.

ssmtp is just MSA (Mail Submission agent).

I have beaten my head against sendmail and postfix enough. They have immense capabilities, but I only need 5% of it. The other 95% just wastes my time and harasses me. As I said, I'm looking for a simplified replacement.

I hadn't heard of OpenSMTPD. Hmmm. They state as one of their goals, "Don't try to support each and every obscure usage case, but cover the typical ones." I'm skeptical, but it might be worth trying. And it's even available in the Fedora repo. Have you used it?

No. I couldn't find one anywhere so I created one.

It's taken me a long time to publish it, but it's finally available on github here: lansmtpd

I don't know if anyone else will want it, but I can't live without it.