Install ruby-premailer by entering the following commands in the terminal:
sudo apt update sudo apt install ruby-premailer
Description:
Preflight for HTML e-mail
This package provides the premailer gem, which helps to improve the rendering of HTML emails by making CSS inline, converting links and warning about unsupported code.
Homepage: http://premailer.dialect.ca/
Version: 1.8.6-2
Section: universe/ruby