cannot install any pkg due to error of FQDN

[Muhammad Usman]

following error comes whenever i try to install any pkg

Your system needs to have a fully qualified domain name (fqdn) in
order to install the var-qmail packages.

Installation aborted.

dpkg: error processing qmail (--configure):
 subprocess installed post-installation script returned error exit status 1
dpkg: dependency problems prevent configuration of qmail-run:
 qmail-run depends on qmail (>= 1.06-2.1); however:
  Package qmail is not configured yet.
dpkg: error processing qmail-run (--configure):
 dependency problems - leaving unconfigured
Setting up otcl-shells (1.14+dfsg-2) ...
No apport report written because the error message indicates its a followup error from a previous failure.
                          Errors were encountered while processing:
 qmail
 qmail-run
E: Sub-process /usr/bin/dpkg returned an error code (1)

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: qmail 1.06-4
ProcVersionSignature: Ubuntu 3.5.0-41.64~precise1-generic 3.5.7.21
Uname: Linux 3.5.0-41-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.0.1-0ubuntu17.5
Architecture: amd64
Date: Wed Oct 23 20:37:48 2013
InstallationMedia: Ubuntu 12.04.2 LTS "Precise Pangolin" - Release amd64 (20130213)
MarkForUpload: True
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: netqmail
UpgradeStatus: No upgrade log present (probably fresh install)