ホスト名：名前またはサービスが不明

2つのパッケージのインストール中にこのエラーが発生します。

root@blackbox:~# apt-get install mpack ssmtp
Reading package lists... Done
Building dependency tree
Reading state information... Done
mpack is already the newest version.
ssmtp is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
2 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] Y
Setting up ssmtp (2.64-8) ...
hostname: Name or service not known
dpkg: error processing package ssmtp (--configure):
 subprocess installed post-installation script returned error exit status 1
dpkg: dependency problems prevent configuration of mailutils:
 mailutils depends on default-mta | mail-transport-agent; however:
  Package default-mta is not installed.
  Package mail-transport-agent is not installed.
  Package ssmtp which provides mail-transport-agent is not configured yet.

dpkg: error processing package mailutils (--configure):
 dependency problems - leaving unconfigured
Errors were encountered while processing:
 ssmtp
 mailutils
E: Sub-process /usr/bin/dpkg returned an error code (1)
root@blackbox:~#