In our company up until now, we've had an on-site Exchange 2007 installation. For the purposes of this question, we have 3 servers :

  • Exchange07MBX01 (Mailbox, Hub Transport)
  • Exchange07MBX02 (Client Access)
  • Exchange07CAS01 (Client Access, Hub Transport)

Currently, all Outlook clients point to Exchange07MBX01, with HTTP proxy enabled pointing to webmail.mycompany.com.

Over the last couple of days, I've installed Exchange 2013 on different VMs. I've updated everything, so the two are successfully co-existing at the moment. The 2013 servers are :

  • Exchange13MBX01 (Mailbox)
  • Exchange13MBX02 (Mailbox)
  • Exchange13CAS01 (Client Access)
  • Exchange13CAS02 (Client Access)

I also setup a hardware load balancer between the two CAS servers, call it Exchange13LoadBalancer. I've also setup the external urls for all my Virtual Directories to be the same as the Exchange 2007 machines, webmail.mycompany.com.

I've successfully moved my own mailbox to the 2k13 servers, by using the Migrate Batch function. I can browse to OWA and access my mailbox.

At the end of the migration, Outlook popped up a message saying that "The Exchange Administrator has made a change requiring you to restart Outlook", which I did. However, no changes were applied. I'm assuming that this change would then point my Outlook Client to one of the new client access servers (my Outlook client still pointed to ExchangeMBX01, with the HTTP proxy pointing to webmail.mycompany.com).

I then took another user, started their migration, added two entries in the host file for :

  • webmail.mycompany.com -> Exchange13LoadBalancer
  • autodiscover.mycompany.com -> Exchange13LoadBalancer

When the migration completed, and asked this user to restart Outlook, still no changes were applied. Once again, when I manually changed it on his computer, it worked fine.

Onto my question... Is there an automatic way (i.e. AD policy/DNS setting/Voodoo) of changing this? Is this the proper way to migrate users to Exchange 2013? I can't change the DNS record for webmail.mycompany.com to point to the new Exchange servers, as their mailboxes are still on the Exchange 2007 servers... or can I?

What is the best way to move their mailboxes, while not requiring me to go to each user's computer and create a host file/change the mail account to point to Exchange2013LoadBalancer/delete the account and make a new account pointing to the new server?


1 Answer 1


Exchange 2013 CAS can proxy/redirect access to your 2007 mailboxes. You don't want the ExternalURL to be the same on CAS servers for both versions though. Your Exchange 2007 servers ExternalURL should be legacy.mycompany.com, and the 2013 CAS servers can continue to use webmail.mycompany.com.

You want to migrate CAS/transport to your new servers first, which will proxy/redirect access to your old mailbox servers. Once you verify that you can access mailboxes residing on the new and old environment and the new environment is handling bidirectional mail flow, you can cut over DNS. Then you can move mailboxes until you've cleared out the 2007 environment, at your leisure.

While I haven't yet done a complex 2007 to 2013 migration, I have done 2007 to 2010 and 2010/2010 site migrations. The following document should give you some helpful guidance around coexistence and how to properly configure it: http://technet.microsoft.com/en-us/library/bb310763%28v=exchg.141%29.aspx

Please let me know if any specific configuration questions come up.

  • In our (inherited) environment, HTTP Proxy is enabled for all Outlook clients. This points to webmail.mycompany.com. If I change the ExternalUrl of the 2007 machines to legacy.mycompany.com, and make the 2013 servers' ExternalUrl webmail.mycompany.com (at the moment they are both webmail.mycompany.com), will the users with 2007 mailboxes still be able to get their mail? Is that what the proxy does pretty much?
    – Marcel
    May 13, 2013 at 10:35
  • You have to have an InternalURL set on the old CAS servers that is reachable internally by the 2013 CAS servers. This will allow the 2013 servers to proxy connections to 2007 mailboxes. Having legacy.mycompany.com as your 2007 ExternalURL will allow redirecting to work. Proxying and redirecting happen in different cases depending on the location of the user, the location of the Exchange servers relative to each other, and the client access method being used. May 13, 2013 at 12:50

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