Emails not sending correctly

We have 2 accounts on the server and emails aren't getting sent correctly from one to the other. The setup we have is; Domain1 - Local mail exchanger Domain2 - Remote mail exchanger When we send an email from domain1 to domain2, it still looks locally on the server and then we get the error message 'No Such User Here'. Is there anything else that I need to change on the server for this to work, so it does send it to the remote mail server? Any help would be very much appreciated! Thanks