Using Xenial I was able to install version 3.1.0-3ubuntu0.2 from proposed and complete the verification steps in the test case. I can confirm that postfix started as expected with the new version, but failed to start with the current version in the archive.
Using Xenial I was able to install version 3.1.0-3ubuntu0.2 from proposed and complete the verification steps in the test case. I can confirm that postfix started as expected with the new version, but failed to start with the current version in the archive.
My log from Xenial is attached