linux: annoying postfix install popup

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When installing postfix, it does a annoying popup. Here's a screenshot:

postfix config screenshot 2013-05-20 1 postfix config screenshot 2013-05-20 2
Linux postfix installation popup screenshot.

Programs shouldn't do this, because it interrupts installation.

For example, this happened when i'm installing emacs dependencies by sudo apt-get build-dep emacs23. 〔☛ Building Emacs on Linux — a Guide〕 I wasn't even consciously installing postfix. You go for a coffee, expecting things will be done when you come back, but instead, you get this popup stuck on your screen.

Another software that does this is MySQL.