Exchange 2003 to Exchange 2010 - CoExistence

Hello Experts,

Some background on the current environment:

150 Mail boxes/ 55 Users
AD=2003 (already prepped for the new exchange environment link updates suppressed)
New mail terminates to Barracuda Spam & Firewall then sent to exchange servers
Exchange= 2003SP2 -
2 backend exchange servers one at headquarters the other at a branch office with a few mailboxes for those in the branch.
1 FrontEnd doing webmail/activesync/rpc-https  (webmail.contoso.com w/ssl)

We are upgrading to Exchange 2010 SP1 (I will install sp3 separately) in Coexistence as we want to move mailboxes over slowly until we are comfortable with the new environment. Here are my questions:

1.      When I install my first exchange 2010 server (CAS/HUB) will that in anyway effect my existing environment. I read that it creates routing connectors to the existing exchange 2003 servers. Will that impact mail flow from just installing exchange 2010?

2.      When installing my first MailBox/HUB will that effect my current exchange environment?

3.      I will using a new public dns name for the CAS (mail.contoso.com w/ssl) as to maintain the existing environment without interruption. I understand that eventually I will be making the 2010 server the primary for mail distribution to users still on 2003 as well 2010 and supports legacy web redirect to the existing front end server. Will the new name cause any issues with this?

I am going to start with a couple test accounts. Any tips or warnings are welcomed!

Thank you sincerely,
Oscar ReyesSenior Systems AdministratorAsked:
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Gareth GudgerSolution ArchitectCommented:
1/. It does create routing connectors but those connectors are only used for transferring mail between 2003 and 2010 servers. So it only affects inter-Exchange mail flow. It does not affect the existing mail flow. As you move users to 2010, mail will flow from the internet, through Exchange 2003 and over the routing connectors to 2010.

2/. It won't affect anything.

3/. No the new name will not cause any issues. The old server will continue to use the old name. You will want to direct all users to use the new name and then set up the CAS Legacy statements, which will auto-redirect 2003 users to the 2003 server automatically.

I highly recommend this article for your migration.
https://www.simple-talk.com/sysadmin/exchange/upgrade-exchange-2003-to-exchange-2010/

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Oscar ReyesSenior Systems AdministratorAuthor Commented:
Thank you, I found that link as well. If i may ask one other question related to exchange:

I never setup an autodiscover before. I had my registrar create a new A record 'autodiscover.contoso.com' i have that pointed to to same public ip as my CAS/HUB which has the A record 'mail.contoso.com

I know there are other steps i need to complete on the exchange server but is this correct from public dns (all will be secured with a san cert)

Thank you!
Gareth GudgerSolution ArchitectCommented:
Looks good. Just make sure you have port 80/443 pointed to your new CAS/HUB server from the firewall. Yes, you will need a UC SAN certificate. In 2010 you create the CSR directly through the Exchange Management Console. You plug in all the services and addresses you plan to use and it tells you what kind of certificate you will need to buy (SAN) and then generates the CSR for you. Process that with a 3rd party provider and install the cert. Then move your IIS services over to it.

https://testconnectivity.microsoft.com/ is a great tool to test your autodiscover configuration is working correctly.
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