Glad you found the probable solution.
Though the question the other user asked regarded sendmail, postfix does need a "human" user designated. Here's the quote from the comments in /etc/aliases:
For various security reasons, postfix WILL NOT deliver mail as root, so
# ensure that the root alias is aliased to a HUMAN user, as otherwise
# mail may get delivered to the $default_privs user (nobody).
I used to use sendmail and had all kinds of trouble getting it to work and stay working. Then I switched to postfix and mutt, after the "mail" command used with sendmail ceased working, and it's been relatively smooth sailing ever since.
This is just for a one-user (me) simple desktop system.