merging 2 organizations and running mail for 2 organizations/domains on one exchange server

Posted on 2013-11-14
Last Modified: 2013-12-19
I have 2 separate organizations, domains, and forests.  They are are linked together by a domain trust.  As of yet I do not have a federated trust between exchange servers. Eventually these 2 organizations will merge into one organization. Basically one will for the most part absorbed the other. Many users of the one organization will be absorbed into the other organization while others will stay with the old organization.  This will include mailboxes.  I want to know if there is a way I can use the Exchange server of the old organization to host old email as well as set up a database etc for the new organization.  basically I would like it to do and Basically I want to continue to use as much of the old infrastructure as possible but transition it to the new company/new domain. I would like to set them up independently, but part of the same domain.  Similar to having an office in NC and an office in MI all part of teh same domain but connected by MPLS.  The great thing about the old organization is that it is across the hall and connected by Ethernet cable.  I know this is somewhat vague as I am not sure how to put into words what I am envisioning.
Question by:dustaine
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Accepted Solution

piattnd earned 500 total points
ID: 39648052
From all my years of knowledge/experience of exchange and mergers, I'd say no, this is not possible (or at least feasible).  All mergers I've been through have established 2 mailboxes for those who are going to merge over, the old and the new.  Eventually, the old goes away and the new becomes permanent and the new email domain takes over the entire old email domain (in case real world senders still have the old information).

The reason I would say it's not possible is because of the way Exchange handles email domains.  The second you tell exchange "you are answering for", it assumes that all addresses exist within the organization, and not outside of the organization, thus it cannot split or determine that ",, and are internal, while,, and are external".  If you sent a message to, your exchange would try to deliver it internally, and fail UNLESS you setup a contact or mailbox to forward those emails to an external domain.

I hope that answers the question. I could be wrong though!  :)
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Expert Comment

by:Simon Butler (Sembee)
ID: 39648055
Technically it is possible. You would need to use Outlook 2010 so you can connect two different Exchange orgs. However the major problem is going to be mail routing, things could get very confusing very quickly.
What you could do is move the users on to the preferred platform, remove Exchange from the old domain, rebuild the server with a fresh installation of Exchange and then move content around.

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Expert Comment

ID: 39648064
What you're referring to Simon (correct me if I'm wrong) is essentially what I said, where you'd migrate the old exchange infrastructure and address space into the new domain, correct?
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Author Comment

ID: 39648167
My thought is that I would need to create a new domain... Company B.local to match what they will be merging into, set up a domain controller and exchange server. then set up routing between the two locations much like I have now, but with a different address space.... 10.0.x.x is my NC location and 10.1.x.x is the home Michigan location. The old company is 10.2.x.x.  I figure I could make the new segment 10.3.x.x Set up the Exchange server to mimic the new organization and set up its users in AD/Exchange.  That way I could make sure the new segment is visible and routing for whenever the go live date will be. I have never merged an organization so this is all new to me. I have set up independent organizations, but that is it.  Thankfully both organizations have very similar setups... All Exchange 2010, server 2008 functional level, all on VM Ware.
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Expert Comment

ID: 39648207
I think you're going through a ton of work for very little gain, but I'm also not too clear on what you're last post was explaining.
LVL 63

Expert Comment

by:Simon Butler (Sembee)
ID: 39648391
You can't migrate the old Exchange infrastructure in to the new domain, because you cannot take Exchange from one forest and put it in to another. The most you can do is use the hardware and licence for a new build.


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