Unixcop published a tutorial about installing the free email server Kolab Groupware on CentOS7.

How to install free email server Kolab Groupware on CentOS7

This post is about How to install free email server Kolab Groupware on CentOS7 Kolab uses IMAP as an underlying protocol for email, contact, and calendar entries. These entries are saved in IMAP folders in Kolab XML format, and the IMAP server controls storage and access rights. 

How to install free email server Kolab Groupware on CentOS7 - Unix / Linux the admins Tutorials