No, I think it has to be a number.
Right. It's on our wishlist - I don't know when we'll get around to it. http://directory.fedora.redhat.com/wiki/Wishlist
uhm, so can you confirm me that to create a new account I have to specify uid and gid in numerical way ? And in this way if mail is 4 example 501 any user with gid 501 is member of mail group?
thanks Alex