Just realized that there is an issue with saving / uploading files to briefcase.
If uploaded filename contains some i18n letters (i.e. ą, ć, ń, ę, ł, ó, ż, ź), the file cannot be downloaded, opened etc..
Zimbra displays error 404, no such element.
If I rename filename to basic letters (ie. ą -> a), everything is OK.
Posted new thread, because I couldn't find any related case on forum.