Yes, you've been annoying me for quite some time now and my patience, finally, ran out! From now on I'll adopt a different solution, simpler, and much easier to configure and work. In fact, it's already working.
The choice, this time, and until it starts annoying me, is an email system that is also native to OpenBSD: it's called OpenSMTPd, and it's the simplest solution I've found so far. And, as you know, simplicity is security's best friend; complexity is the real foe.
This system isn't very old, it's been developed by several people who are part of the OpenBSD team, and is aimed mainly at simplicity and security for email servers.
It's not the top of its class – nor does it seem to want to be – as regards features. It doesn't have as many features as sendmail and the like. However, for organizations whose context is medium or small, well, it's more than enough.
That being said, to avoid closing this note without mentioning some other useful things, I'll leave you the direction to the manual pages of the program and the configuration file. They're are: (i) smtpd and, most important, (ii) smtpd.conf. There : )
Finally, as there is no beauty without flaws, the settings that I've set up now, as far as I could see, limit all security flaws that regard open relaying, all but one (not a serious one, though). And the flaw is: I cannot stop someone from sending messages like
nobody (at) miguelalmeida (dot) net for
somebody (at) miguelalmeida (dot) net. This doesn't make it an open relay, of course, but it's still a wrinkle (which isn't important for me, but I would prefer if it wasn't there).
Email filters are still missing in this setup. I'll keep posting the news, if any, whenever ; )