Some computers have been processed by QMM RUM (Resource Updating Manager) and moved to the target domain. While the target domain already has accounts and mailboxes created for these users, they are still logging into the source domain with their source credentials. Upon launching Outlook users no longer have the same Outlook 2007 profile settings. The following pop up messages may be encountered by migrated users when they launch Outlook 2007 on their machines:
"The Microsoft Exchange Administrator has made a change that requires you quit and restart Outlook"
"Your mailbox has been temporarily moved on Microsoft Exchange server. A temporary mailbox exists, but might not have all of your previous data. You can connect to the temporary mailbox or work offline with all of your old data. If you choose to work with your old data, you cannot send or receive e-mail messages"
Further examination shows that the source mail profile is now pointing to the target Exchange 2007 server while EMWProf was never executed. How to explain and remediate this behavior?

The issue is caused by the fact that computers are joining the target domain located in the new forest with an Exchange 2007 organization. In this case the source users log into their machines, that are already in the target domain and Outlook 2007 Autodiscover finds the SCP (SERVICE CONNECTION POINT) containing target Autodiscover URL. As a result Microsoft Exchange 2007 Autodiscover process initiates and reconfigures the Outlook profile to point to the target Exchange 2007 server.

IMPORTANT: It was determined during testing that DisableAutoStartup and ZeroConfigExchange registry parameters from HKCUSoftwareMicrosoftOffice12.0OutlookAutoDiscover HAVE NO AFFECT on the current issue. They are simply changing Outlook behavior with regards to the new MAPI profile configuration when the “Add new E-mail Account” wizard comes up. If a MAPI profile is already configured – Autodiscover cross-forest mailbox move logic is utilized which is based purely on an XML it receives via the AutoDiscover process.

WORKAROUND 3
1.     Close Outlook 2007
2.     Open regedit
3.     Open HKCUSoftwareMicrosoftOffice12.0OutlookAutodiscover
4.     Add a new DWORD: «PreferLocalXML» = 1
5.     Add a new REG_SZ: «Right-part of SMTP address for you  source mail» for example «source.domain.com» = path of a new file (XML) that you are going to create for example «C:Program Files (x86)Microsoft OfficeOffice12OutlookAutoDiscoversource.domain.com.XML»
6.     Add a new REG_SZ: «Right-part of SMTP address for you target mail» for example «target.domain.com» = path of a new file (XML) that you are going to create for example «C:Program Files (x86)Microsoft OfficeOffice12OutlookAutoDiscovertarget.domain.com.XML»
7.     Create C:Program Files (x86)Microsoft OfficeOffice12OutlookAutoDiscoversource.domain.com.XML file.
8.     Create C:Program Files (x86)Microsoft OfficeOffice12OutlookAutoDiscovertarget.domain.com.XML file.
An example of XML file is attached to the article.

WORKAROUND 4
It was also reported by the field engineers that following registry modifications from http://support.microsoft.com/kb/956297  and changing all the values listed there to 1 resolves this issue.

Useful Tips:
1. In order to determine if Autodiscover URL resolves properly please hold Ctrl and then right click on the Outlook Icon and select "Test E-mail AutoConfiguration ...". Uncheck "Use Guessmart" and "Secure Guessmart Authentication" as they have no much value in the corporate domain environment and then click Test. The resulted screen will show what settings have been discovered by Outlook 2007. "Log" and "XML" TABs will contain the discovery steps and XML for the mailbox configuration if any.
2. Additional logging can be enabled in Outlook 2007 as follows: Tools | Options | Other | Advanced Options...| Enable logging (troubleshooting). When performing Autodiscovery as described in #1 the log is created under %temp% directory.

IMPORTANT: The workarounds mentioned in this article are not official suggestions or recommendations and are published only as attempt to assist migration admins when making decisions and looking for possible workarounds. Quest support will not be able to assist with troubleshooting any issues which might arise when using these suggestions.
Attached is Outlook Automatic Account Configuration.doc Microsoft White Paper that contains very detailed information on how Autodiscover Outlook 2007 service works. Also please check these additional Microsoft resources:

"Autodiscover and Exchange 2007"
http://technet.microsoft.com/en-us/library/bb232838.aspx

Troubleshooting Free/Busy Information for Outlook 2007
http://technet.microsoft.com/en-us/library/bb397225.aspx

More information about these Outlook 2007 registry parameters can be found here:
"Deploying additional registry values in the Office Customization Tool for Outlook 2007"
http://technet.microsoft.com/en-us/library/cc837949.aspx