In the first part of this article we identified our requirements for moving from a single Exchange 200x server to a coexistence configuration. We identified the need to retain OWA public folder access and third party Exchange 2003 applications functionality.
So far we walked through the installation of Exchange 2007, ending up with two servers running in separate routing groups. In this second part, we conclude the upgrade so that to meet our initial requirements.
Moving Mailboxes to Exchange 2007
Before starting to move mailboxes, we relocated the store databases to a different drive. This is done from the Exchange 2007 Management Console under Server Configuration | Mailbox, right-click the database and select 'Move Database Path'.
Next we moved one mailbox from Exchange 2003 to Exchange 2007. This is done from Recipient Configuration | Mailbox, right-click the mailbox and select 'Move Mailbox'.
From the first wizard step we selected the destination Exchange 2007 Mailbox Database.
This wizard also allows for specifying whether the move should proceed in case of corrupted messages.
With a few more clicks on the Next button the move was completed.
We were now able to test email flow between the two servers and confirmed the Routing Group Connectors were working correctly.
SMTP Connector - Controlling Email Flow
One important pre-requisite from the new configuration was to retain the third party applications running on Exchange 2003. These email hygiene applications necessitated access to all incoming and out outgoing internet email. This meant that Exchange 2003 had to act as the only internet bridgehead. Consequently the Exchange 2007 Edge server role was not installed and instead focused on getting email routing right.
Incoming email flow did not necessitate any changes. The DNS settings were already pointing at the Exchange 2003 machine. From there, emails were routed to the Exchange 2003 mailboxes (we still did not move all mailboxes at this stage) and to Exchange 2007 mailboxes through the Routing Group connector without problems.
On the other hand outgoing emails to foreign domains from the Exchange 2007 mailbox were not being delivered. In Exchange 2007, internet emails are typically routed through an edge subscription connecting the Hub Transport to the Edge Transport server. Otherwise it is also possible to create a Send connector for the Hub Transport to directly deliver outgoing internet email. Edge subscriptions and Send Connectors can be created from the Exchange 2007 Management Console under Organization Configuration | Hub Transport.
However none of these applied to our case since we wanted email to flow outbound via Exchange 2003. To understand the problem let's see how emails were delivered outbound before the upgrade. Exchange 2003 simply relied on the SMTP Virtual server which resolved the destination via DNS and delivered the emails. The Virtual server configuration is really not important here. The important point is that Exchange 2003 did not make use of connectors for outbound email delivery. However now that we had two Exchange servers, we needed an SMTP connector to identify the one acting as a bridgehead to the internet.
The connector must be created within the Routing Group where the Exchange 2003 is a member. Other than that, there was nothing special.
At the Exchange 2003 ESM browse to:
First Organization | First Administrative Group | Routing Groups | First Routing Group | Connectors
Right-Click Connectors and select New | SMTP Connector
Give the Connector a name and click Add to configure the Exchange 2003 SMTP Virtual Server as the bridgehead
Next move to the Address Space property page and click Add. To route all internet bound email, choose the SMTP address type, set the domain to * and cost to 1.
Now that the connector is in place all servers know how to route emails to foreign domains. To confirm this, move to the Exchange 2007 configuration console. Under Organization Configuration | Hub Transport | Send Connectors a new connector should now be visible for the SMTP Connector just created.
With the email routing configuration cleared, following some tests we proceeded with moving all remaining mailboxes. OWA users will now be happy to discover the new Exchange 2007 functionality. Furthermore OWA public folders access is still available from the Exchange 2003 machine. Note that with the upcoming Exchange 2007 SP1 it is expected that Exchange 2003 won't be needed for this purpose any longer.
The Exchange 2003 third party applications were not concerned of the final email destination as long as these were routed through them. Thus we were also able to retain their functionality. Of course different applications have different requirements and one should check with the application vendors whether such a solution would work for them as well.
The coexistence configuration does present a more complex Exchange configuration environment. However it has key advantages that are worth considering. Apart from the specific benefits highlighted in this article, coexistence allows a more gradual upgrade process.
Exchange 2007 SP1 is expected to fill a number of functionality gaps. Organizations who are missing some features, may find that instead of waiting, coexistence provides the best way forward.
Upgrading to Exchange 2007 (Part 1)
Managing Outlook Web Access Virtual Directories in Exchange 2007