[rt-users] Allowing a 'group' of customers to see certain ticketsin a queue

[Oliver Marx]

Dear List,

We have the following problem:

User_A is user_a at company1.com
User_B is user_b at company1.com 
User_C is c_user at another_company.com

User_A sends in a ticket - #1
User_C sends in a ticket - #2
User_B sends in a ticket - #3

Both User_A and User_B should be able to see ticket
#1 and ticket #3 but  _not_ ticket #2.

User_C should be able to see ticket #2, but not
tickets #1 and #3.

Is this possible to do with RT3, and if so, how does  one do it? 

\Oliver