Now I have successfully installed Zimbra 8.6 FOSS on Centos 7 64bit. I noticed that Postfix is still installed on the system (the service is disabled).
[root@mail ~]# rpm -qa | grep postfix
[root@mail ~]# service status postfix
The service command supports only basic LSB actions (start, stop, restart, try-restart, reload, force-reload, status). For other actions, please try to use systemctl.
[root@mail ~]# service postfix status
Redirecting to /bin/systemctl status postfix.service
postfix.service - Postfix Mail Transport Agent
Loaded: loaded (/usr/lib/systemd/system/postfix.service; disabled)
Active: inactive (dead)
The reason why I want to remove it is because for some strange reason, the root user still keeps on receiving email
Will I break anything is I remove Postfix server still keeps on receiving mail!