How to have a cross forest mailbox in Exchange 2010

active-directoryexchange-2010

I have two forests, forest A, forest B.

Forest A has no Exchange server.
Forest B has 2010 Enterprise.

Forest A does not trust Forest B.
Forest B does trust Forest A.

The users are in Forest A, and I want Forest B to use those users in A and give them mailboxes in the B Exchange server but authenticate with A's domain controller.

Is this possible? If so how can I do it?

I cannot use Federation Services because I only have one 2010 Exchange server and it is in Forest B.

Thanks.

Best Answer

Obviously, without the caveat information (which I'll happily update this answer with) my gut instinct is to say you need to build a 'resource forest'. Effectively, what this does is it allows users from one Forest access Exchange resources within another forest. This can be used effectively when two companies merge but have no desire to restructure their AD forests. This TechNet article will walk you through setting up Exchange in this fashion.

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Exchange 2010 – Number of Mailbox Databases

Spreading out your mailboxes across databases is good to keep database sizes low. If anything goes seriously wrong and you have to run offline utilities to get things back, you will thank yourself for keeping smaller databases. Users do not like being without email for the 8 hours it takes to recover a 25GB database.

As for targeted moves, there is a way to move users into specific databases. We did this when we did the 2003 > 2007 move. I believe you need to use Exchange 2010 tools to do the migration, and you can pick the target database. We used a PowerShell script to perform the migrations, which may expose a few more controls to manage this.

Exchange 2010 SP1 Prepare-MoveRequest.Ps1 cross forest migration

There are two switches that will allow merging when users exist in the target domain. In my case the source and target account names were different, so I required an include file for ADMT, but for this preparemove I specified Identity using smtp address which it recognized in source and target and did the merge perfectly based on that.

They are -UseLocalObject followed by -OverwriteLocalObject

.\Prepare-MoveRequest.ps1 -RemoteForestDomainController dc401.dc.contoso.com 
-RemoteForestCredential $RemoteCredentials -LocalForestDomainController phiads001.dt.inc -LocalForestCredential $LocalCredentials -UseLocalObject -OverwriteLocalObject -Verbose -Identity wbrown@contoso.com

VERBOSE: Local ad account with dupplicate proxy addresses found: CN=Woody Brown,OU=Users,OU=Philadelphia,DC=dt,DC=inc
VERBOSE: Merging Mailbox properties to local MailUser
VERBOSE: Setting msExchMailboxGUID to 136aef07-5869-415e-ae0e-bbe69963593b
VERBOSE: Setting proxyAddresses to x500:/o=DealerTrack/ou=Exchange Administrative Group
(FYDIBOHF23SPDLT)/cn=Recipients/cn=Woody Brown8d2 x500:/o=DealerTrack/ou=Exchange Administrative Group
(FYDIBOHF23SPDLT)/cn=Recipients/cn=Woody Brown753677056d53 X400:c=US;a= ;p=contoso;o=Exchange;s=Brown;g=Woody;
SMTP:wbrown@contoso.com
Appending x500:/o=contoso/ou=First Administrative Group/cn=Recipients/cn=wbrown to proxyAddresses of Object(CN=Woody Brow
n,OU=Users,OU=Philadelphia,DC=dt,DC=inc) in Local forest.
VERBOSE: OverwriteLocalObject specified. Updating MailUser with with attributes from source MBX(CN=Woody
Brown,CN=Users,DC=dc,DC=contoso,DC=com).
VERBOSE: Setting displayName to Woody Brown
VERBOSE: Setting Mail to wbrown@contoso.com
VERBOSE: Setting mailNickName to wbrown
VERBOSE: Setting msExchMailboxGuid to 136aef07-5869-415e-ae0e-bbe69963593b
VERBOSE: Setting countryCode to 0
VERBOSE: Setting givenName to Woody
VERBOSE: Setting Sn to Brown
VERBOSE: Setting textEncodedORAddress to c=US;a= ;p=contoso;o=Exchange;s=Brown;g=Woody;
Preparation for wbrown@contoso.com done. Local recipient info Merged.
1 mailbox(s) ready to move.
[PS] C:\scripts>

Best Answer

Related Solutions

Exchange 2010 – Number of Mailbox Databases

Exchange 2010 SP1 Prepare-MoveRequest.Ps1 cross forest migration

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