Zimbra is an easy to use piece of unified collaboration software. Being one of the best free, open source collaboration software available, Zimbra includes email, calendaring, file sharing, activity streams, social communities and much more! Zimbra comes in two different forms: a free open source edition and a paid version.
I have 8G of Ram 0=disable 1=enable
If Ram = 4GB, set the value to 512M
If Ram = 8GB, set the value to 1024M