package postfix 2.10.0-2 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1

[Nick Moffitt]

When upgrading from quantal to raring, postfix fails to configure because it lost its main.cf. This seems like it ought to be a file installed by the package, but:

 dpkg-query: no path found matching pattern /etc/postfix/main.cf.

ProblemType: Package
DistroRelease: Ubuntu 13.04
Package: postfix 2.10.0-2
ProcVersionSignature: Ubuntu 3.8.0-13.23-generic 3.8.3
Uname: Linux 3.8.0-13-generic x86_64
ApportVersion: 2.9.2-0ubuntu1
Architecture: amd64
Date: Tue Mar 19 13:47:36 2013
DuplicateSignature:
 Setting up postfix (2.10.0-2) ...
 postconf: fatal: open /etc/postfix/main.cf: No such file or directory
 dpkg: error processing postfix (--configure):
  subprocess installed post-installation script returned error exit status 1
ErrorMessage: subprocess installed post-installation script returned error exit status 1
MarkForUpload: True
SourcePackage: postfix
Title: package postfix 2.10.0-2 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1
UpgradeStatus: Upgraded to raring on 2013-03-19 (0 days ago)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.