Add users to Active Directory user's Mailbox Rights property in c#

hi All I am working upon Active Directory objects, i can search a user, get the list of users/computers etc. but i am not finding any solution in following case I need to Grant full access privilege of a AD user's mailbox account to any other AD user so that he can access that user's account with his own credential. Manually it is done by accessing the Mailbox rights of the user and no. of users can be added to whom we want to give that user's Mailbox access. My requirement is to do it by c# code. Any help will be appreciated. Thanks in Advance.