In the current Linux-Magazine there’s an article by Markus Feilner on grommunio. Sadly, the printed migration script will not work with the grommunio-Version that is on the DVD. Where the article describes the August 2021 version of grommunio, the version on the DVD has been updated and adapted specially for the Linux-Magazin by grommunio.
This archive file has the correct, updated and tested new version of the script: http://www.feilner-it.net/files/exchange2grommunio.zip