Obviously Apache is not setup to use the proxy-module to pass requests for the URL /sac/ to tomcat. You dont need to setup a VirtualHost, but you should setup the proxy-module or proxy_ajp module for apache or connect to tomcat directly on its port (8080)
requests are handled by tomcat only. Have a look at the output of "netstat -tlpn | grep java" to find out if and at what ip/interface tomcat is listening (usually port 8009) and try to setup apache so that it passes through these request using either mod_proxy.
Tomcat can be integrated into apache in different ways - either tomcat is running standalone so you can connect - usually via port 8080 - and try
http://localhost:8080/sac as well as
http://localhost:8080/webmail (for ip/hostname and port that tomcat might listen to have a look at netstats output)
If tomcat does not work at all, have a look at /var/opt/scalix/your_instance_name/tomcat/logs/scalix-caa.log and catalina{DATE}.log to find out more about what might be the problem.