I am not expert in hMailserver so my question might look silly for you

I have a case where user2 emails forwarding set to user3, suppose user1 is sending an email to user2 and mark user3 in CC then user3 getting 2 number of copies.
Example:
1) User2-->Forwarding set to-->User3
2)User1-->Email-->To: User2, CC: User3
3) User3 receiving 2 copies of same email
Can you please help me setting a RULE in hMailServer so that only one copy of emails would be deliver (Unique email Delivery based on message ID)