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My company is currently using Microsoft Exchange Server 2007 and wants to upgrade to 2010. My company has about 100 employees and a large flow of email messages in every hour.

Read from Microsoft article (, an extra domain is required for the co-existence when both servers are running.

As creating an extra domain is complicated, is there any quicker method that does not require an extra domain?

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As far as I can tell that article states that you need to create a new DNS host name, not a new domain name. – joeqwerty Oct 11 '10 at 11:22
up vote 5 down vote accepted

A sub domain of your already existing domain name is a perfectly acceptable (and recommended) way of doing this.

The article suggests you use legacy.yourdomain.tld for your Exchange 2007 server and yourdomain.tld for the Exchange 2010 server. That shouldn't involve much more than creating a new DNS A record for your legacy sub domain and modifying the existing record to contain the new Exchange 2010 server.

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Considering that the upgrade from Exchange 2007 to 2010 is a lot more complicated than change a few DNS entries, this should be the the least of the worries :) – tegbains Oct 26 '10 at 4:59
I agree the dns entries are the least of your worries. But, not having to do another public certificate to add can avoid some complexity. – Brian Dec 14 '10 at 18:23

What the document is referring to is the address of the external access methods for the old and new environments. Exchange 2007 (and 2010) involves certain specific hostnames so clients can figure out how to access the Exchange environment. autodiscover.yourdomain.tld is used to figure out what IP address or hostname a client needs to locate the Client Access server(s). This needs to point to an Exchange 2010 Client-Access server so long as you have Exchange 2010 in your environment.

This server will proxy requests to legacy.yourdomain.tld. If a user hits OWA (which is on an Exchange 2010 Client-Access server) but still has their mailbox on an Exchange 2007 mailbox server, it will proxy their requests to the Exchange 2007 Client-Access servers by way of the legacy hostname. Therefore, it is important that the 'legacy' address point to the 2007 Client Access servers.

Once you've moved everyone to Exchange 2010 mailboxes, there is no need to have the Exchange 2007 Client-Access servers. At that point, 'legacy' is no longer needed.

The key thing to keep in mind is that these are hostnames not domains.

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