Mysterious "unable to resolve host" in dead.letter

Question

In the ~ directory of the root user on my debian wheezy server regularly appears file named dead.letter with (currently) the following content:

orion : Jul 25 10:17:31 : root : unable to resolve host orion

orion : Jul 26 02:17:18 : root : unable to resolve host orion

orion : Jul 26 21:17:19 : root : unable to resolve host orion

orion is the hostname of the server (and can normally be resolved since I have various services/programs using this hostname without problems). After some searching I figured that there is a cron job running hourly, i.e.

17 * * * *  root    cd / && run-parts --report /etc/cron.hourly

which could explain why those errors only appear 17 minutes after the full hour. The only script in /etc/cron.hourly is fake-hwclock with the following content:

#!/bin/sh
#
# Simple cron script - save the current clock periodically in case of
# a power failure or other crash

if (command -v fake-hwclock >/dev/null 2>&1) ; then   
   fake-hwclock save
fi

Can this produce those mysterious dead.letter? And why seems fake-hwclock save try to resolve the hostname?

---

Edit: Some more information.

Input of /etc/hosts:

127.0.0.1       localhost
::1             localhost ip6-localhost ip6-loopback
fe00::0         ip6-localnet
ff00::0         ip6-mcastprefix
ff02::1         ip6-allnodes
ff02::2         ip6-allrouters

Answer 1

Change the following line in /etc/hosts

127.0.0.1       localhost

to

127.0.0.1       localhost  orion

Your MTA was unable to resolve the domain name of your machine.

Answer 2

Jodka Lemon's answer is correct:

• cron executes its job, and sends a result mail to "root@orion" (via "mail" or similar)
• the MTA cannot resolve host orion, since the hostname is not listed in /etc/hosts and not resolvable via dns.
• so the mailer writes the dead letter information

You will find the destination address of crons mail output in the crontab file which holds the /etc/cron.hourly entry. This sould be /etc/crontab, I think...

Have Fun ... Gerhard