Comment 19 for bug 1519331

The only workaround I could get to work was to restart postifx on network up by adding `/etc/network/if-up.d/999local` with the following contents:

```
#!/bin/sh -e
# Called when a new interface comes up
# Local workarounds

# Fix postfix boot up issue:
# https://bugs.launchpad.net/ubuntu/+source/postfix/+bug/1519331
service postfix restart >/dev/null 2>&1
```