This is not a question, but simply a post so that this info is available via archives / search engines for anybody running into an issue I had recently. No courier specific search queries returned the necessary results, so here goes...

If you are running courier esmtpd and after sending an email you get an error response like this:

550 Don't like your HELO/EHLO. Hostname must contain a dot.

It is NOT a courier installation issue, but rather the way the hostname is configured for the machine courier is running on.

If you execute the "hostname" command, and just get:

foo

instead of:

foo.bar.com

...the simplest thing to do (at least on a SuSE 9.2 machine) is to execute, as root:

# hostname foo.bar.com

Verify:

# hostname foo.bar.com # hostname -s foo

No courier specific configuration should be necessary.