Giving your (admin) account the “postmaster” alias doesn't actually do anything because /etc/postfix/aliases hardwires postmaster to root and that sends mail to /dev/null. I fixed this by setting the “root” config var in aliases.
In other news, watch out for failed user-specific crontab entries. Sometimes (more than once) running
> crontab -u user -e
will simply hang, creating a tmp.something into /var/cron/tabs. This drives cron mad, eating up all the cycles it can. To fix is to basically pull a:
$ rm -rf /var/cron/tabs/tmp.*
$ killall cron -SIGHUP