Install claws-mail-managesieve by entering the following commands in the terminal:
sudo apt update sudo apt install claws-mail-managesieve
manage Sieve filters with Claws Mail
This plugin for Claws Mail mailer provides an interface for managing filtering scripts on Sieve-compliant mail servers. . It allows creating new, editing and removing existing server scripts. Syntax checking is also available, but knowledge of filtering language is required.