Zimbra (ZCS) is an open source and free for personal use, collaborative software platform. Let's see how to install it on Ubuntu 18.04
How To Install The Zimbra Desktop Email Client On Ubuntu 8.04 LTS (Hardy Heron)
Install Zimbra 8.8 on Ubuntu 20.04, 18.04, 16.04
Install Zimbra 9 on CentOS 7 / RHEL 7 / Ubuntu 18.04
How to Install Zimbra Collaboration 8.8 on Ubuntu 16.04 LTS - Zimbra : Blog
Install Zimbra on Ubuntu 20.04 Step by Step - inGuide
Zimbra: Instalando Zimbra 9 sobre Ubuntu 18.04 LTS, paso a paso y vistazo a la nueva Modern Web App - El Blog de Jorge de la Cruz
How to install Zimbra on Ubuntu 18.04 LTS
Let's setup Zimbra 9.0.0 on Ubuntu 18.0.4 and configure letsencrypt SSL certificates on it - Postbox Consultancy Services
How to Install Zimbra 8.6 on Ubuntu 14.04 Server
Mailchimp Email Marketing Guide
Install The Latest Zimbra OSE (8.8.15) On Ubuntu 20.04LTS
Chandan Pawar, Author at Postbox Consultancy Services
How to install Zimbra on Ubuntu 18.04 LTS
Install Zimbra Desktop on Ubuntu 18.04 Bionic Beaver