Creating a common mailbox

Hi,

can anybody help me to solve the below scenario?
1.Create a common Mailbox say ?Archiving Team?. and give access to following members X,Y,Z.restrict “delete” permission to all members except ‘W’ or an IT administrator. Also all members should have permission to ?Read, Reply, Forward, Move (to another folder within the Mailbox) etc.i did this but..i’m facing prob in restricting members to delete mails and folders.
Thanks.