Users not 'mail enabled' ? can't change 'mail' ldap attribute ?

Users not 'mail enabled' ? can't change 'mail' ldap attribute ?

I need to bulk modify the 'mail' smtp attribute of my users so that servicedesk sees their email addresses. If I try to use the exchange tab to do it, it doesnt return any users under 'mail enabled.'
 
I can modify the 'mail' attribute under 'custom attributes' in modify users, but i cant tell it %givenName%1%sn%  like I can under the exchange side.  Help !

                    New to ADSelfService Plus?