Share permissions

Hi

I have a share which is used for email. The share contains folders named after each member of staff. I would like to know how I can enable all users access to the share, but only allow a user to access their folder.

E.G. The share name is Mail. Sub-folders are named John, Sarah, Richard etc. I want to allow John, Sarah and Richard access to the Mail share, but I only want Sarah to be able to access the Sarah folder, and not be able to access to John or Richard folder.