file permissions

[Ryan Mayor <ryan mayor utoronto ca>]

Hello all, 

I am trying to setup an ftp server with an /incoming directory.

How do I set the file/folder permissions for this directory so that all
users in group ftp can create subdirectories and upload files, but not
download or delete them.

Is this possible?  I have been staring at man chmod for the past hour...

Thanks!

-Ryan