I could have had troubles on my system from unwanted users knowing about my set up, because I did not set my emails in /etc/mail/aliases. I think that the editting of this file should be mentioned in the manual in the "Finalizing your Gentoo Installation" section. If you need more details concerning how it can be dangerous for /etc/mail/aliases to not be edit, feel free to ask.
*** This bug has been marked as a duplicate of 125396 ***