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+Create folder for RainLoop in `mailcow-dockerized/data/web` 
+Download installer.php and run it from php docker container. 
+Remove installer.php
+Login servername/rainloop/?admin
+Change password from 12345
+```
+cd data/web
+mkdir rainloop
+cd rainloop
+curl -s http://repository.rainloop.net/installer.php >> installer.php
+# run php file from php docker image, which should be already running along others. 
+# your container name might be different from mailcowdockerized_php-fpm-mailcow_1 -
+# use `docker ps` to find out
+
+docker exec -it mailcowdockerized_php-fpm-mailcow_1 php /web/rainloop/installer.php
+
+       [RainLoop Webmail Installer]
+
+
+ * Connecting to repository ...
+ * Downloading package ...
+ * Complete downloading!
+ * Installing package ...
+ * Complete installing!
+
+ * [Success] Installation is finished!
+
+rm installer.php
+```
+
+**login servername/rainloop/?admin to changepassword** and setup connection to mailcow
+
+In domain section add desired domain
+IMAP dovecot
+SMTP postfix
+Secure STARTTSL on both