there is installed 'postfix'. So what you need is to check configuration(mx entries, smtp server) and start-up the daemon. After that, your '
mailx -s "subject" "firstname.lastname@example.org" should work as used to.
Getting no error is normal, because postfix is trying to deliver your email for few days, so it is severity 'warning' not 'error', check /var/spool/mail/root (or issue 'mail' command on shell ; and you will see the pending mails) for more details (or if you are sending it from some "td_user" check /var/spool/td_user instead). If you do not run 'postfix', you should recieve info from 'postdrop' utility (that configuration is not right).
By default you can send email(s) within the vmware box/localhost.localdomain only. So when testing and developing script you can send email from root to td_user normally without any reconfiguration. As this is working for me without touching any config files:
mailx -s "TEST" -a "test.data" "root@localhost"