mailcow-dockerized-docs/docs/third_party-rainloop.md

1. Create a new subdirectory for rainloop and download the RainLoop installer:

mkdir data/web/rainloop
curl -o data/web/rainloop/installer.php -s http://repository.rainloop.net/installer.php

2. Run the installert from within the PHP-FPM mailcow container:

docker exec -it $(docker ps -qf name=php-fpm-mailcow) php /web/rainloop/installer.php

3. Login to ${MAILCOW_HOSTNAME}/rainloop/?admin to set a password

Add and configure a new domain as you need.