Coexistence of Exchange 2003 and Exchange 2010 - Using Exchange 2003 as a routing server

Just wanted some advice please.

Here's my current setup.....

Two main servers:

AKT01 – Domain controller (Active directory\dns\dhcp) (MS Windows 2003 Std)
AKT02 – Exchange server (MS Windows 2003 Std / Exchange 2003 server enterprise)

We now need to upgrade our current setup to MS Windows 2012 as OS and MS Exchange 2013 server

Step: 1 Migrate DC\AD to Windows 2012 to new hardware (AKT-01). This step we are able to do as we have done this in testing environment.

Step: 2 Deploy Microsoft Exchange Server 2010 in an existing Microsoft Exchange Server 2003 organization operating in native mode. Coexistence with these two Exchange.

I am comfortable with the step 1. However with step 2 I would like to progress this in hops to get to exchange 2013. For now I need to concentrate on moving 2003 to 2010. This is where I need help\assistance……

My question:

Can  I carry on using both exchange (2003/2010) server and route all emails via exchange 2003 whilst I gradually move mailboxes (circa 300 mailboxes) over to exchange 2010? And then decommission 2003.

Ideally I would like to route inbound\outbound email via exchange 2003 once the mailboxes has been migrated over to 2010.

On my test environment I’ve been able to make the mail flow between two exchange servers but I need to know if I can make the exchange 2003 as routing email server out to internet even though the mailboxes resides on the 2010?

Also would it affect the OWB\OMA if it was routed out via 2003? Our SSL certificate currently is assigned to 2003 for OWA & OMA.

Your assistance is much appreciated.

Kind regards,
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AmitIT ArchitectCommented:
AD to 2012, is fine. As far as coexistence with 2003 and 2010. Yes, you can use 2003 for mail routing. However, I would suggest to use 2010. Install 2010 in your environment. If you want to install for test only, then create new Site in AD and then install Exchange 2010. This way you can avoid issue for your 2003 users. Once you feel 2010 is ready, you can move it to production site.

I personally would suggest you to move to 2010 and then move over to 2016 directly. 2016 is out in the market and much simplified.

Let me know, if you still have any query.

Use these tools

Note: Server sizing is very important. Install multi-role server. For Exchange 2016 watch this video:
AKTIIAuthor Commented:
Hello Amit,

Thanks for your response and suggestions. For time being i need to upgrade to 2010 and route all emails via 2003 until I've migrated all the mailboxes over, as this is critical to the business i want make sure there's no downtime. Can you advice me on how do i go about this?

Many thanks,
Seth SimmonsSr. Systems AdministratorCommented:
migrate to exchange 2010 first and do your domain later
exchange 2003 does not support 2012 domain controllers

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