package ssmtp 2.64-7 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1

When I try to install , am getting this issue. so please help me on this.

ProblemType: Package
DistroRelease: Ubuntu 14.04
Package: ssmtp 2.64-7
ProcVersionSignature: Ubuntu 3.13.0-53.89-generic 3.13.11-ckt19
Uname: Linux 3.13.0-53-generic i686
ApportVersion: 2.14.1-0ubuntu3.11
AptOrdering:
 postfix: Remove
 ssmtp: Install
 ssmtp: Configure
Architecture: i386
Date: Fri May 22 16:46:14 2015
DuplicateSignature: package:ssmtp:2.64-7:subprocess installed post-installation script returned error exit status 1
ErrorMessage: subprocess installed post-installation script returned error exit status 1
InstallationDate: Installed on 2015-01-09 (132 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release i386 (20140417)
SourcePackage: ssmtp
Title: package ssmtp 2.64-7 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1
UpgradeStatus: No upgrade log present (probably fresh install)