package postfix 3.0.4-3 failed to install/upgrade: subprocess new pre-installation script returned error exit status 1

[Kev Bowring]

Normal update and upgrade today I get postfix failing to upgrade.

ProblemType: Package
DistroRelease: Ubuntu 16.04
Package: postfix 3.0.4-5
ProcVersionSignature: Ubuntu 4.4.0-7.22-generic 4.4.2
Uname: Linux 4.4.0-7-generic x86_64
ApportVersion: 2.20-0ubuntu3
AptOrdering:
 postfix: Install
 postfix: Configure
 NULL: ConfigurePending
Architecture: amd64
Date: Sat Feb 27 13:50:20 2016
DuplicateSignature: InvalidHostOrDomain
ErrorMessage: subprocess new pre-installation script returned error exit status 1
EtcMailname: *** /etc/mailname does not exist ***
Hostname: wolf
InstallationDate: Installed on 2015-10-29 (121 days ago)
InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Alpha amd64 (20151029)
PostconfMydomain: Error: command ['/usr/sbin/postconf', '-h', 'mydomain'] failed with exit code 1: /usr/sbin/postconf: fatal: open /etc/postfix/main.cf: No such file or directory
PostconfMyhostname: Error: command ['/usr/sbin/postconf', '-h', 'myhostname'] failed with exit code 1: /usr/sbin/postconf: fatal: open /etc/postfix/main.cf: No such file or directory
PostconfMyorigin: Error: command ['/usr/sbin/postconf', '-h', 'myorigin'] failed with exit code 1: /usr/sbin/postconf: fatal: open /etc/postfix/main.cf: No such file or directory
RelatedPackageVersions:
 dpkg 1.18.4ubuntu1
 apt 1.2.3
ResolvConf:
 # Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
 # DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
 nameserver 127.0.1.1
 search Home
SourcePackage: postfix
Title: package postfix 3.0.4-3 failed to install/upgrade: subprocess new pre-installation script returned error exit status 1
UpgradeStatus: No upgrade log present (probably fresh install)

[Apport retracing service (apport)]

Thank you for taking the time to report this crash and helping to make this software better. This particular crash has already been reported and is a duplicate of bug #1531299, so is being marked as such. Please look at the other bug report to see if there is any missing information that you can provide, or to see if there is a workaround for the bug. Additionally, any further discussion regarding the bug should occur in the other report. Please continue to report any other bugs you may find.