This script extracts calendar entries out of a maildir and puts them into one org mode file. This is based on ical2org and uses part of its source code.

Right now it expects ical2org to be installed locally

$ pip3 install --user ical2org
$ git clone https://github.com/bkoppelmann/mbox2org.git
$ ln -s mbox2org/mbox2org.py ~/.local/bin/

Give it a maildir folder with --folder and a path with --output where the org file should be created.

$ mbox2org --folder <maildir> --output <cal.org>