I recently installed postfix but I did something wrong. And so I removed it with sudo apt-get remove postfix and removed the /etc/postfix folder.
But now I want to install it again but I don't get the installer prompts where I can choose Internet Site and other options. How can I solve this?
That's because there are still some files in place and dpkg considers the package to be configured.
There are two possible routes you can take to solve this:
sudo apt-get purge postfix, then re-install and the config dialog should come up.dpkg-reconfigure postfix