How do I forward outbound mail for a specific user in postfix?

I want to create a rule that forwards all mail with a specific sender to another email address.

From what I can tell, this might be possible with sender_bcc_maps but I can't find any examples using a specific address, only domain matches.. additionally, the user does not exist in postfix, this is simply an outbound relay server (on a static IP, in a datacenter) for another Exchange server (on a dynamic ip, in an office).

From serverfault gregmac

• Ended up adding to main.cf:

  sender_bcc_maps = hash:/etc/postfix/outcopy
  

  and then /etc/postfix/outcopy:

  from@domain.com copyuser@anotherdomain.com
  

  then ran:

  postmap /etc/postfix/outcopy
  /etc/init.d/postfix reload
  

  and it is working.

  From gregmac