Had to update to MariaDB 5.5 via YUM manually, then install postfix. Still would not work from xenForo (and neither would the smtp setup). Once I finally figured out that maybe I needed to set the sendmail_path to the /usr/lib/sendmail-postfix (which I did) did it start working.
I'm used to Debian - where there are no hoop-jumping like the above required. Install your DB flavor of choice, install nginx, install php5-fpm and related, install postfix and then fine tune (but it works without having to remove sendmail, update the MariaDB, etc, etc.).