According to this log, postfix is running. Please restart postfix, if it failed, post the log entrys that have been added to the mail log.
Updating ispconfig first and then running yum for instance, results in an unusable system.
This order does not work as yum overwrites the configuration and makes the system unusable. The other way, updating centos first and then ispconfig works as ispconfig trys to repair the files that yum has overwritten.