postfix configuration popup on default install path confuses users

Doug Smythies brought this up as note in another bug - thanks Doug.
I confirmed and checked the backgrounds a bit and now split it out to a separate bug.

Postfix gets installed by default these days on the server images - the dpkg --configure popup of postfix can confuse users that didn't think/plan/expect a mail server.

The reason it is installed can be found on a freshly installed system with
  apt-cache rdepends [--no-{suggests,conflicts,breaks,replaces,enhances}] --installed --recurse postfix
    cron => suggests: exim4 | postfix | mail-transport-agent
    libsasl2 => breaks postfix <= 2.8.3-1
So it has only two dependencies, but none that forces an install.
Thereby it has to be in the seed itself.

There is an indirect dependency, see http://people.canonical.com/~ubuntu-archive/germinate-output/ubuntu.xenial/server
You can see that it is in because of a recommends from mdadm - it does in fact recommend "default-mta" and the germinate output at
http://people.canonical.com/~ubuntu-archive/germinate-output/ubuntu.xenial/_germinate_output
reports "Chose postfix out of default-mta to satisfy mdadm"

But as I checked, Germinate did so back to trusty - but there didn't install postfix as mdadm was not part of the server seed.

IMHO it is correct that mdadm made it into the server seed and by that it is only logical that postfix gets pulled in as well.
But I wanted to ask if maybe there is a way to silence postfix on that default install path - so that users that didn't think/plan/expect a mail server are not confused by that?