Mail routing between two global domains

Please let me know how can i display the internet address when email are sent between two global domains (two global domains document)

i.e

I have two global domain documents

  1. abc.com

  2. xyz.com

when user1@abc.com sends a mail to user2@xyz.com I want the user2 to see the other person’s address as user1@abc.com. NOT AS User1/OU/O/DOMAIN.