Mail was accidentally installed on my debian server and I want to remove all mta, mail related software. I do not know what exactly was installed, how can I find out and uninstall this stuff? I don't want to see this "you have mail" when I log in.
dpkg --get-selections | grep -v deinstall
for a shorter list, which shows you what is installed. Look through the list, work out the major packages you don't need (like exim, postfix, mailx, bsd-mailx, etc.) and then,
apt-get remove exim mailx ......
I'm assuming you're using postfix since it's the default mail server for Debian (I think). You should be able to remove this by using:
apt-get remove postfix
If it's not the postfix package just substitute the name of the package that was installed.