FileSharing/Briefcase sharing in RW mode with foreign domain

[blason]

Hi Folks,

Is it possible to share folder in RW mode with foreign domains or email addresses. Folder sharing is pretty much possible with foreign domain however opposite party would not be able to add or download the file. Can that be possible in briefcase, I need share my few folders or files with my trusted Business Partners however they are on separate domain and facing issue while sharing file. If not through briefcase is there any other alternative through zimbra that folder/file will be shared.