According to http://wiki.kolab.org/Kolab_3.0_Storage_Format#Annotations wh have these rules:
# Folders with mail content MAY exist without metadata.
# Folders without any metadata MUST be treated as mail folders.
# Folders with an unrecognized folder-type annotation SHALL NOT be displayed to the user as containing normal mail data.
the problem is now if we have the following situation:
```
"Spam": {"/private/vendor/kolab/folder-type": "mail.junkemail", "/shared/vendor/kolab/folder-type": ""}
```
-> rule 1 does not match there is a shared annotation
-> rule 2 does not match the shared annotation exists -> no mail folder
-> rule 3 matches -> folder is not displayed
but this is not the intended behaviour isn't it?