I have been trying to automatically install postfix in a non-interactive way via startup-script on machine boot up.
After a bit of research I found out some suggestion that I could try to install it manually on a sample machine using desired configurations then obtain the right answers regarding configurations when startup-script will be running by using
debconf-utils package command debconf-get-selections | grep postfix >preseed.cfg
The problem is with one configuration which is the mailname that is due to the fact that my instance machines are generated in a non predetermined manner by the gcp cloud host I can not tell in advance which name to pass as I initially pass the first config selection as:
debconf-set-selections <<< 'postfix postfix/main_mail_type string "Local only"
Now the question is how could just leave the default value? (which one could see had it been an attended installation and simply click ok to finish up)