Oh and he removed my handly added $myhostname form amavisd.conf. Is it what he should do when updating?
Yes, thats intended as the updater installs the correct config files for ispconfig. Setting the hostname in amavisd.conf is not nescessary if the server is installed correctly. If you had to change it there then this indicates that your server has no fqdn. You should check that the hostname is configured correctly in centos so that the commands:
and hostname -f
show the correct fully qualified domain name of the server.