Install dovecot-metadata-plugin by entering the following commands in the terminal:
sudo apt update sudo apt install dovecot-metadata-plugin
Experimental IMAP METADATA Extension for Dovecot
This is a set of plugins for the Dovecot IMAP server version 2.2 that implement the IMAP METADATA Extension. The goal of the development is to extend dovecot so that it can be used as the IMAP component instead of Cyrus IMAPd in the Kolab server.