If you need to know which version of Zimbra is running on your server, use steps described below
Connect to your Zimbra server using ssh
$ ssh zimbra-host
Switch to zimbra user
$ su – zimbra
run this command to get Zimbra version
zimbra@zimbra:~$ zmcontrol -v
Release 8.7.11.GA.1854.UBUNTU16.64 UBUNTU16_64 FOSS edition.
Hope it helps !