Zentyal is an open source Linux-based server for small and medium-sized businesses. It is a unified network infrastructure solution that combines the most popular open source technologies such as Samba, Postfix, OpenLDAP, Squid, and others into a single, easy-to-manage platform. It provides small business owners with a secure, reliable, and cost-effective alternative to proprietary solutions. Zentyal is designed to be simple to use, yet powerful enough to serve as the server for a wide range of businesses. It can be used for file and print services, LDAP and Active Directory authentication, email, proxy and web filtering, as well as other network services. Additionally, Zentyal provides a web-based graphical user interface (GUI) to make it easier to configure, manage, and monitor the server. Zentyal is ideal for small and medium-sized businesses that need an affordable, secure, and reliable network infrastructure solution.
I used it for my personal mail server and nextcloud. In addition, I used it with BgLUG (http://bglug.it/scuole) in our "Linux in schools" project as primary domain controller on the school IT lab servers. Very nice distribution: efficient and easy to use.