I just found a great article that discussed about the difference between xen and open vz. Here is the link.
Month: September 2009
Sender verify defer + host lookup did not complete
Login to WHM >> Main >> Service Configuration >> Exim Configuration Editor .
Uncheck the option:
Sender Verification
If it doesn’t help, reset ALL EXIM configuration to default and try again.
Install Zend Optimizer
cd /usr/local/src
check latest zendoptimizer
wget http://www.eth0.us/files/ZendOptimizer-3.0.1-linux-glibc21-i386.tar.gz
tar -zxf ZendOptimizer-3.0.1-linux-glibc21-i386.tar.gz
cd ZendOptimizer-3.0.1-linux-glibc21-i386
./install
If u still receiving “Zend Optimizer Not Installed” error page, then
SELinux is interfering with Apache’s attempt to access the .so file.
So do this commands
#chcon -t texrel_shlib_t path_of_ZendOptimizer.so (/usr/local/Zend/ZendOptimizer.so)
#execstack -c path_of_ZendOptimizer.so (/usr/local/Zend/ZendOptimizer.so)
#setenforce 0
#getenforce
then restart httpd and check.
If the issue still persist,
vi /etc/selinux/config
SELINUX=disabled
then reboot the server