Currently I have an unorthadox setup where I have my mx records going to a third party email host where I have set up all users with an email address to this domain, from there I have set a cc: to my exchange 2007 server using a secondary smtp address for my exchange users. Out of all users of this domain 80% of the users are on the third party host and never touch my exchange server, and 20% are actual exchange users.
Email comes into the third party host and is delivered to all of my users with no issue except for any email sent from the users from within the network. Since there is no email address for 80% of our users on the system the emails get rejected and a NDR is produced.
I am new to Exchange 2007 however there was a way in Exchange 2003 to set the domain so it wasn't exclusive to the domain allowing it to send the emails outside the exchange server which in this case would allow all emails to be delivered to the third party host.
Please let me know if you can lead me in the right direction to resolve this issue.