Exchange Cross Forest Connectors with shared email domain

StevenRB used Ask the Experts™
We have two forests, one has exchange 2003 servers and the new one we are migrating to has exchange 2010. We need email for our one email domain to flow between the exchange 2003 and exchange 2010 servers and vice versa so as users are moved to the new forest - email still works for them. Two way trust is working. I have a send connector setup for internal in the on the exchange 2010 server which is working and email to recepients on exchange 2003 is going through. (Exchange 2010 is set to non authoritative for the email domain).
On exchange 2003 I have an SMTP connector pointing to the exchange 2010 server. Exchange 2003 is set as authoritative for the email domain -but when I send to recipents in the exchange 2010 forest I get: email account does not exist 5.1.1 error. If I change the exchange 2003 to non auth for the email domain, external users get rejected receipient errors 'unable to relay' when sending to the email domain. Can anyone help us to get this working ?

Thanks in advance
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Madan SharmaConsultant

here is link for how to create routing connectors between exchange servers in cross forest


Yes that's the document I followed - but it hasn't worked.
ok if that is not working for you then you can try the following:-
1. add your domin as accepted domain on exchange 2010 as internal relay
2. point mx record for the domain to exchange 2010

check this link also:-

on exchange server create new send connector and send all mails via exchange 2010 as smart host.

Hope this will help you...
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Thanks for that - but the email domain we use has to go to the exchange 2003 servers at the moment.


Doesn't look like I have a choice so I will redirect email to the 2010 server - thanks for your help
I realize this may be a bit late, but if you're still having trouble with this, the solution is actually quite simple.  What you need to do is create contacts in each of your forests with name and e-mail addresses corresponding to the users in the opposite forest.  You will need to delete the contact in the target forest before you migrate your users and mailboxes and then re-create the contact in the source forest once the migration has completed.  You will have to continue doing this until all your users have been migrated to the new forest at which point you need to make sure your new Exchange server is set as authoritative and you can then disable the send connectors on both Exchange servers and sever the forest trusts to confirm all sending is working properly (if it's not, just re-enable your trusts and send connectors to maintain communication while you figure out what you might have missed).

You will want to maintain the x500 addresses for the mailboxes of all users being migrated to the new forest as failing to do so will cause delivery failures as you move forward.

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