Single email address for head office and branch office

Hi Experts,
I have been working on a requirement to consolidate our exchange environment, meaning that we have four branch offices reporting to head office, and each branch office has got different domain and different email address & exchange servers are consisting of exchange 2010 and exchange 2013. Now our management intends to have a single email address for all offices, and eventually all the email address will be managed by head office using exchange 2010 environment.
User1@ Branchoffice1.com
User2@ Branchoffice2.com
User3@ Branchoffice3.com
User4@ Branchoffice4.com
User5@Headoffice.com
Now I need to migrate all the users (User1@ Branchoffice1.com, User2@ Branchoffice2.com, User3@ Branchoffice3.com, User4@ Branchoffice4.com) to headoffice.com
Though we have a plan to consolidate active directory infrastructure latter this year but at his moment, management wants us to apply single email address for all users.
I need your advise how can I plan for the implementation steps, could you please validate the following procedure and advise.
1.      Establish AD trust between headoffice.com to branchoffice1.com to brachoffice4.com since branch office users will be using headoffice.com email address, sitting in branch office AD.
2.      Need to create all new mailboxes for branch office users in headoffice.com with same address @headoffice.com
3.      Need to set a forwarder from branchoffice1.com to headoffice.com for new user mailboxes.
4.      Export existing PST from branch office mailbox and import to new outlook mailbox (headoffice.com)
5.      Change the MX record to Branchoffice1.com to heaoffice.com
6.      Disable the forwarding from brachoffice.com to headoffice.com
ipsec600Asked:
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Peter HutchisonSenior Network Systems SpecialistCommented:
1. This is easy to do using AD Domains and Trusts and a reliable network connection between the branches.
2. Also, fairly easily to do.
3. There are many ways to do this,
a) Setup Transport rules to auto-forward mail to the branchoffice.com addresses.
b) Setup individual contact users in AD with the new email address and then configure the Delivery options on each old banchoffice mailboxes to auto-forward mail sent to the old mailbox to go instead to the contact address and thus to the new branchoffice address.
4. It may be possible to avoid PSTs, and just use the Remote Move Mailbox feature in Exchange 2010 to offsite Exchange services. It depends whether you want to keep the old mailboxes in place, until all users are moved.
5. No, need to change the MX record, you just keep the existing ones and create a new headoffice.com mx record.
Delete the old mx records, when all mailboxes have been moved.
6. Delete the old Transport forward rules or contacts and old mailboxes when users are moved.
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Simon Butler (Sembee)ConsultantCommented:
"5. No, need to change the MX record, you just keep the existing ones and create a new headoffice.com mx record.
 Delete the old mx records, when all mailboxes have been moved."

I disagree with that step.
Depending on the business, there could be senders who only communicate infrequently. Therefore the old email addresses should be applied to the new accounts, with the MX records moved to the new server as well (so the branch office email domains are added to the accepted domain list). That will ensure that anyone using the old email addresses will continue to have the email delivered, but replies will go out on the new addresses. I would be looking to retain the old email addresses for at least 12 months.

The forwarding method is an excellent idea, and that is what I would do. Leave the forward in place until all mailboxes have been moved, then switch the MX records.
Furthermore you should add the old email address to the new accounts before the MX records are moved. That will ensure that any internal users who send email to the old addresses (Which will happen) get delivered straight to the new mailbox.

Simon.
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Peter HutchisonSenior Network Systems SpecialistCommented:
Yes, that seems reasonable to do.
The old email addresses can be transferred to the new mailboxes so that the old and new email addresses still work, the MX records would just need changing to the final Exchange transport servers.
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ipsec600Author Commented:
Apology that I was not available.

Thank you Peter and Simon for your excellent clarification.
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