I need kind of strategic advice. I am in course of building a mailing application serving for an advertising agency having multiple customers. Strict separation of all customers-related files is a must. So, because the mailing can have embedded images and attachments - I really need an isolated containers (folders?) for all stuff uploaded to the server. What is the right strategy to implement such a file manager, so it only allows browsing and uploading files to programatically-defined server folder? Please feel free to share ideas!