Most of this data has been imported from kdepim originally with the messagetreeparser. The .tree and .html files are anecdotal only.
To generate new gpg encrypted content use an existing mime message to your liking, and then copy in ascii armored content in. The encrypted content can be created using:
gpg2 --home /src/kube/framework/src/domain/mime/mimetreeparser/tests/gnupg_home/ -a -r test@kolab.org --encrypt toEncrypt.txt
where toEncrypt.txt contains the to be encrypted content.