As information in release notes that Instant Messaging (IM)/Chat not available in Zimbra 8. The following is information in release notes Zimbra 7
Zimbra Instant Messaging (IM) capabilities are going to be removed in the next major release of ZCS. These capabilities include the embedded IM server and the Zimbra IM Client (part of the Zimbra Web Client). Zimbra IM is marked BETA and should not be enabled in a production environment and is not a supported feature.
I know this information has been there in 2/3 year ago. However, many of my clients still use Zimbra 7 and use IM/Chat as secondary communication besides email. If you want to enable IM feature in Zimbra 8, please try this guidance
cd /srv/ wget -c http://www.zextras.com/download/zextras_suite-latest.tgz tar -zxvf zextras*.tgz cd zextras* ./install.sh all
Select Y (Yes) on every question and wait until done. Perform the following command to flush cache as root user
su - zimbra -c 'zmprov fc -a zimlet'
Please login to Zimbra Admin. Select ZeXtras Suite | ZxChat. Click Deploy to install zimlet ZxChat.
# Configure users to use ZxChat (add buddy list)
After zimlet ZxChat deployed, invite/add buddy all users to use ZxChat. Login to Zimbra Admin. Select ZeXtras Suite | ZxChat. Enter distribution list that have member all users. If you do not have distribution list, please create. Or you also can add ZxChat between two users to each others buddy list. Press connect this group/these accounts. Please see the example below
Please login to webmail. You will see the ZxChat already to use
Good luck and hopefully useful 😀