How to migrate exchange users from one domain to another domain

I need to migrate number of mailboxes (20 to 25 only) from one of our sister companies ( belongs to exchange 2010 into our internal domain ( in exchange 2010. We are not intended to establish trust between two domains ( and ( Just intend to migrate their mailboxes from to but once the migration will be performed then users from will be using their email address/mailboxes sitting in my exchange servers (
1.      Need to migrate 25 users from to
2.      Users from will use my exchange servers ( but their email address and mailboxes will be
Need guideline what could be the migration steps I will have to consider. (MX record pointer change, mailbox export etc). Would you kindly assist to know the steps or any appropriate link that might help me!!
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imkotteesSenior Messaging EngineerCommented:

1. Create a mailbox for them
2. Export their pst and copy to your domain
3. Import it with new mailboxes

For same email address, you can put them all in a single OU and create a Email address policy as you want.

Changing MX record is needed when you are completely (all the users) moving all of them to new domain. if you are doing partial you should not do that.
SandeshdubeySenior Server EngineerCommented:
Cross Forest Migration Guide – Exchange 2010 to Exchange 2010
ipsec600Author Commented:
Hi  Sandeshdubey, thank you for your post, actually i am not intended to do cross forest migration cause i will not be able to perform trust between domain.
Hi Sandeshdubey, thank you for your post, but I am not doing cross forest migration since i am not able to do the trust between domain.

Hi imkottees,

Thank you so much for your guideline, would you kindly assist to know the followings:
1. Create a mailbox for them
Ok, Should I create mailboxes for 25 users as to, cause objective is to migrate to in our

2. Export their pst and copy to your domain

3. Import it with new mailboxes
How I will import .pst of to, cause users ,pst is from, would you please clarify more.

4. For same email address, you can put them all in a single OU and create a Email address policy as you want.

OK. I will create single OU and create email address policy and apply that policy on that OU, and will create "Accepted domain" for in our exchange server.

5. Changing MX record is needed when you are completely (all the users) moving all of them to new domain. if you are doing partial you should not do that.
Yes, we will completely move all the users to new domain, once the above steps will be completed(1,2,3,4) then we will change MX record and point MX to exchange servers, but during transition period email will be lost or it will be in queue, and what would be the best time to shutdown the email server?
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imkotteesSenior Messaging EngineerCommented:
1. you need to create an accepted domain for and then need to create a email address policy for this domain. Finally create a mailboxes by keeping users in this domain.

3. there wont be any problem with domain.

4. Yes, you can't create an email address policy w/o accepted domain.

5. i would suggest this.
5.1.  Create all new mailboxes here in with same address

5.2. Set a forwarder from to user mailboxes

5.3. Create an email address policy for in internaldomain (should not be primary at the moment)

5.4. change the MX record to (they will be able to receive emails as it is added into secondary email address list)

5.5. make email address policy is the primary for OU

5.6. Disable the forwarding from domain

5.7. Ask users to use new mailbox (this can be given to them earlier, its up to you)

P.S: Make sure you are exporting and importing the LegacyDN value into new mailboxes. Else you will receiving NDR when replying to old emails.

I hope this would help.

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Use the Active Directory Migration Tool (ADMT) included on your Windows Server 2003 CD-ROM to move Active Directory objects such as user, computer, group, and OU. MoveTree should only be used in special cases to handle objects (such as contacts) which cannot currently be migrated by ADMT.
Refer the article:
ipsec600Author Commented:
Hi Pankaj_401, thank you for your reference link.
Hi imkottees, thank you for your excellent clarification to attend the issue, and surely its been outstanding help for me to get a clear picture of the scenario. Lastly once again requesting on the   LegacyDN value, is it mandatory part of this migration, and if so, would you kindly provide me any useful link to perform that..
imkotteesSenior Messaging EngineerCommented:
Hi, You are welcome.

LegacyDN value is important if your users are choosing these users (25 of them) from the local outlook cache. Because outlook use LegacyDN value to send email.

Get-Mailbox -ResultSize Unlimited | Ft Name, LegacyDN |Export-CSV c:\LegacyDN.csv

ipsec600Author Commented:
Hi imkottees, thank you once again you are just awesome!!!!!
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