It would be nice if it is possible to archive a whole account or just selected mail folders to a dedicated directory, by saving each mail in the same folder structure like displayed in Thunderbird.
So that it get's easy to include this directory in regular disk backups and easily browse that directory with the file manager of the given OS. And each mail is then represented by one .eml file with the Subject as title. This way it would also be possible to open this emails in 30+ years with an editor or XML Viewer etc when there is not a backward compatible version of Thunderbird available.
But please keep the convention of allowed characters for file names under Windows and Linux, because e.g. rsync get's problems with characters like „<>“.
Thank you very much guys!!! From now on I'll donate yearly 🙂