Setting up Mail Routing between a Exchange 2003 and Exchange 2010 server & the Internet

We've installed Exchange 2010 into our environment.  What is the best way to setup mail routing between both servers and getting mail to and from the Internet?  Should I leave Exchange 2003 to be the transport server to the Internet or make the Exchange 2010 server (running all 3 primary roles) be the transport server receiving directly from the Internet?  
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Schnell SolutionsSystems Infrastructure EngineerCommented:

The best thing is this:

1. While you install and prepare your Exchange 2010 servers. (It includes the routing group connector between Exch 2003 and Exch 2010) left the send connector function in the hands of Exchange 2003

2. After everything is alright with Exchange 2010, when you have more than the 10% of your mailboxes migrated to Exchange 2010 them you can make a new send connector with the exchange 2010 source servers. At this time you will be working with both connectors (Exch 2003 will use its connector and Exch 2010 its connector)

3. After you have most of your mailboxes in Exchange 2010 you can delete the send connector used by Exchange 2003

The general recommendation is to try that most of your Internet messages DO NOT go by the Routing Group connector between Exch 2003 and Exch 2010. The same rule apply for the configuration of your Receive connector. Configure the Exchange server receiving the emails from the internet depending of which organization actually has more users? Exchange 2010 or Exchange 2003. It means that at the beginning all your emails will enter by Exch 2003, and when you have at least the half of your users in Exch 2010 you will configure your Exch 2010 servers to receive the emails from the Internet

ChocolateRainAuthor Commented:
We really don't have that many users.  About 150.  Schnellsolutions, your solution seems like it would make sense if we had 1000s of users as the migration wouldn't take all that long.  With so few users would it be possible to simply point my firewall to the Exchange 2010 server for the email domain and have it route between it and the legacy server until all my mailboxes are moved?  I wouldn't think so but let me know.
You need to read the following MS Technet article which covers the whole migration.

If you had installed Exchange 2010, it would have asked you if you had any legacy servers on your network, had you answered yes, then it would create the legacy connector between the Exchange 2003 and 2010 box for you.

If the connector isn't there, you can create one by following the command on the following link:

It would also by default route all messages through your Exch 2003 send connector, don't forget to create another send connector to route any traffic out from the Exch 2010 box. Yes you can point port 25 traffic to the Exch 2010 box, providing the two servers can talk to each other and aware of each other.

Hope this helps.

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Schnell SolutionsSystems Infrastructure EngineerCommented:

Hello ChocolateRain,

In your case, with few users (and considering that they are standard users) you can just configure your Exchange 2010 server to receive all the Internet email. Exactly like you say. There is not problem with it, the traffic passing the connector is not very relevant

We can say that you can configure your emails receptions at any time during the migration process

ChocolateRainAuthor Commented:
This is the command we ran to re-setup the 2003 to 2010 connectors.

New-RoutingGroupConnector -Name "Interop RGC" -SourceTransportServers "exch2010.domain.lcl" -TargetTransportServers "exch2003.domain.lcl" -Cost 10 -Bidirectional $true -PublicFolderReferralsEnabled $true
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