Planning Corporate Merger of Exchange

We are in the process of merging 4 companies together. For the focus of this question, our concern is to create a solution to utilize a single domain address, with the least amount of work for phase 1. Long term solutions will be adopted during phase 2.

Environment:, 15-25 users, POP Mail, Web/Hosted (will be host starting phase 2), 100 users, Exchange 2010, Server 2008 R2, 50-75 users, Exchange 2010, Server 2008 R2, 50-75 users, Exchange 2003, Server 2003

At the launch of Phase 1, all companies will adopt the domain address

Our initial thought is to start with putting the existing users into an exchange environment. We could export/import their existing mail into a new mailbox hosted on the mail server.

From there, it seems to be a matter of configuring each companies Exchange server to share an SMTP address space. Is this correct?

At each location would we add a SMTP address and set as primary?

Would we point all of our MX records to exchange server?

Thanks for the help!
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mray77Author Commented:
Antonio VargasMicrosoft Senior Cloud ConsultantCommented:
So if i understand correclty:

corp1 exchange 2010 will host the entire solution?

all users should be migrated to the corp1 server?

If all users will have as primary e-mail address. on phase 1 you should configure all 3 exchange environments (corp1, 2 and 3) with the domain as non authoritative. The MX records should point to the corp1 server. and you should configure the shared namespace on every exchange environment. In this scenario all mails to will go into the corp1 server, and if the recipient is not there it will send it to another mail server (corp2 or corp3). This is done for coexistence. Is that what you intend to get here?
Because you have 3 environments you need to test and see if you dont get loops in the mail forwarding process. Also the current 15-25 users must be set on the mail server. it's the best approach as they are very few users and without exchange you wont get coexistence.
mray77Author Commented:
Corp1 exchange 2010 will not initially host the entire solution during phase 1, that is being planned for phase 2 due to time constraints. Does that sound like a good idea?

Currently each company; aside from the smallest that we will build mailboxes for, is capable of operating from their existing exchange server, and we assumed that for simplicity, we would keep that intact during phase 1.

Ownership wants us to utilize one common domain address starting day 1 (phase 1). We are basically absorbing the domain address from the smallest company; which is not currently operating in an exchange environment.

So, configure each exchange environment with domain as non-authoritative, and point the MX records for domain to exchange server, correct? Then configure the shared namespace on every exchange environment. That's exactly what i was thinking in terms of mail flow, corp1, then corp2, then corp3. This is exactly what we need initially.

We have couple extra domain addresses we are going to setup for just 1 user at each location, and see how it works. That will be our test. Sound like a good idea?

Thanks so much!

During phase 2, all users will be migrated to the corp1 server, yes.
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Antonio VargasMicrosoft Senior Cloud ConsultantCommented:
so if all existing exchange servers will continue to operate, you just have to add the domain as an aditional e-mail address on those systems (not primary) and configure the shared namespace on all environments.

yes you can test with an aditional domain. point the mx records to the exchange, and then test the shared namespace configurations for that namespace. dont forget to test it with external and internal e-mails. Mails should flow when sent internally as well. It sounds like a very good idea.

if you need some extra help or have some extra questions let me know.
mray77Author Commented:
Great. Thanks! I will keep this active while we setup a test. I won't forget to assign points!

I've gone through many different mergers like this and wanted to share my thoughts on this.

If the AD domains are going to remain separate during the migration, you will run into autodiscover issues with Exchange 2007/2010 and Outlook 2007/2010.  Outlook will automatically search for due to the primary SMTP address on that user, when in reality his email account resides on's exchange server.  There are work arounds for that, and if the ultimate goal is to have one shared AD and Exchange environment, this would be OK for the short term.   I'm currently working with a client who has two business units that are completely seperate AD domains trying to share the same SMTP namespace long term, and it's not pretty with over 1000 users.

If in the long term the AD structure and companies will remain separate,  I would look at using a subdomain
so,, with MX records for each subdomain pointing to the respective servers.
Antonio VargasMicrosoft Senior Cloud ConsultantCommented:
Auric1983. he wont have a problem with autodiscover with corp3, because exchange 2003 wont use autodiscover service. But you are right, on a coexistence scenario autodiscover needs to be pointed to the corp1 server, and the primary e-mail address of the corp2 users needs to remain the same and cannot be change to Because only on phase 2 the primary e-mail address will be to everyone (right?) and also on phase 2 he will have all mailboxes migrated to one single exchange environment (right?) i guess that this will be just a temporary problem.

BTW autodiscover problems can cause issues like OOF and the download of the offline address book errors, and also prevent outlook automatica configuration from taking place.
There are hacks and registry keys you can deploy to force the autodiscover URL to point to the correct server, its a pain.

But you are right, autodiscover is tightly integrated to the exchange web services, so calendaring, out of office etc. will break.
mray77Author Commented:
We setup a test domain, pointed MX records to exchange, as non-authoritative. I've also added an SMTP address for to an existing mailbox. This is working as expected internally/externally.

The next step is configuring the shared namespace on each mail server, correct? Do we need to wait until we have established VPN connectivity with each other?
mray77Author Commented:
I mistyped, we actually setup the test domain as Authoritative, and i'm expecting the other exchange domains will set theirs up as non-authoritative. Only one can be authoritative, correct? Thanks!
Antonio VargasMicrosoft Senior Cloud ConsultantCommented:
You will need to specify a public or private ip address on the send connector, for the other exchange server, when setting up the shared namespace.
No server can have the domain as authoritative. if you have it as authoritative the mail wont be sent to another mail server if the mail address doesnt exists there.
mray77Author Commented:
Ah, thank you for clarifying authoritative. That makes perfect sense.

What about the other mail servers then, do they just need to configure the SMTP address and domain on their server? They are using Exchange 2003, so they don't have a receive connector to configure. They just need to allow from my public IP correct?
Antonio VargasMicrosoft Senior Cloud ConsultantCommented:
they need to allow their smtp virtual server to receive connections from your server IP. They need to have the domain as non authoritative as well. and they need to create a send connector to forward the mail for that domain namespace to your server.

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mray77Author Commented:
Great. Thanks so much for the ongoing support. We sincerely appreciate it!
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