When my WHM/cPanel installation automatically updated to 11.36 (from 11.34), it silently uninstalled postfix. Took me a while to figure out what was going on. I know that postfix isn't supported, but I've had this setup running just fine for a while. I disabled Exim in WHM/cPanel and had setup postfix on my own. I eventually traced it to the Exim RPM installation. Even though it is disabled, it uninstalled postfix. cPanel should not automatically uninstall postfix.