These are install requirements that I personally use when I'm playing with lab/production Zimbra open source mail servers: - CentOS OS (minimal ISO) - base OS for Zimbra installation from https://www.centos.org/download/ - 8GB+ RAM, 10GB+ HDD, 2+ vCPU Zimbra installation: DISABLE POSTFIX FROM BASE CENTOS INSTALL WHICH COMES BY DEFAULT - systemctl stop postfix / systemctl remove postfix disable iptables firewall - assumes you have some other firewall at public side for your mail server set selinux adequately at /etc/sysconfig/selinux setup local DNS adequately at /etc/hosts - you must resolve domain names which you are going to use in mail server so that system successfully works - even installer checks for resolvable hostname via DNS tar xzvf [zcsfilename.tgz] - unpack previosly downloaded file from https://www.zimbra.com/try/zimbra-collaboration-open-source/ cd [zcsfilename] ./install.sh - begin installation process and follow required steps type X to see complete