I got a special request of a user:
allow a user to upload files, see the files but do not allow them to download any of the stored files. (So you can share 1 account to many but they are not allowed to download those files with that same account).
The master user of that vhost is allowed to control the whole upload folder.
It took me a good dinner to find an appropriate proftpd.conf setting. Some tests performed and it’s working now .