Comment 10 for bug 1727699

Based on the insight that this was added to 3.x but post Xenial being released I provided a fix to be tried in ppa [1].
An associated merge proposal for the packaging is up for review at [2]

[1]: https://launchpad.net/~ci-train-ppa-service/+archive/ubuntu/3095
[2]: https://code.launchpad.net/~paelzer/ubuntu/+source/postfix/+git/postfix/+merge/335622