Outlook 2007 unexpectedly connects to an on-premise Exchange Server 2007 server mailbox instead of an Exchange Online server mailbox

An Outlook 2007 client unexpectedly connects to an on-premise Exchange Server 2007 server mailbox instead of an Exchange Online server mailbox. Therefore, the information that is provided by Autodiscover will be incorrect.
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This problem can occur if the following conditions are true:

• The Outlook client computer is running Outlook 2007.
• The on-premise Exchange server is running Exchange Server 2007.
• Mailboxes on Exchange Online and the on-premise Exchange Server 2007 server use the same primary SMTP e-mail address.

To resolve this problem, follow these steps:

1. Do the following:
   1. Make sure that the latest service pack for Outlook 2007 is installed on the computer. To do this, connect to the Windows Update web site at http://www.update.microsoft.com, and then download and install the latest Microsoft Office 2007 service pack.
   2. Reconfigure Outlook for use with Microsoft Online Services by using the Microsoft Online Services Sign In Application. To do this, follow these steps:
      1. Sign in to the Microsoft Online Services Sign In Application.
      2. On the Options tab, click Advanced Options.
      3. Click Reconfigure my desktop applications.
      4. Click to select the Microsoft Office Outlook check box (if it is not already selected).
      5. Click Configure applications.
   After you perform this step, determine whether the issue still exists. If the issue is resolved, you do not have to perform step 2. If the issue persists, go to step 2.
2. Modify the registry by setting the following registry values in the following registry subkey:
   HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\AutoDiscover
   Value name: PreferLocalXML
   Value type: DWORD
   Value data: 1
   
   Value name: ExcludeHttpRedirect
   Value type: DWORD
   Value data: 0
   
   Value name: ExcludeHttpsAutodiscoverDomain
   Value type: DWORD
   Value data: 1
   
   Value name: ExcludeHttpsRootDomain
   Value type: DWORD
   Value data: 1
   
   Value name: ExcludeScpLookup
   Value type: DWORD
   Value data: 1
   
   Value name: ExcludeSrvRecord
   Value type: DWORD
   Value data: 1
   Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
   322756 How to back up and restore the registry in Windows
   To modify the registry, follow these steps:
   1. Click Start, click Run, type regedit, and then click OK.
   2. Locate the following registry key:
      HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\AutoDiscover
   3. Right-click AutoDiscover, point to New, and then click DWORD Value.
   4. Type PreferLocalXML, and then press ENTER.
      
      Note If the PreferLocalXML value already exists, go to step e.
   5. Right-click PreferLocalXML, and then click Modify.
   6. In the Value data box, type 1, and then click OK.
   7. Right-click AutoDiscover, point to New, and then click DWORD Value.
   8. Type ExcludeHttpRedirect, and then press ENTER.
      
      Note If the ExcludeHttpRedirect value already exists, go to step i.
   9. Right-click ExcludeHttpRedirect, and then click Modify.
   10. In the Value data box, type 0, and then click OK.
   11. Right-click AutoDiscover, point to New, and then click DWORD Value.
   12. Type ExcludeHttpsAutoDiscoverDomain, and then press ENTER.
       
       Note If the ExcludeHttpsAutoDiscoverDomain value already exists, go to step m.
   13. Right-click ExcludeHttpsAutoDiscoverDomain, and then click Modify.
   14. In the Value data box, type 1, and then click OK.
   15. Right-click AutoDiscover, point to New, and then click DWORD Value.
   16. Type ExcludeHttpsRootDomain, and then press ENTER.
       
       Note If the ExcludeHttpsRootDomain value already exists, go to step q.
   17. Right-click ExcludeHttpsRootDomain, and then click Modify.
   18. In the Value data box, type 1, and then click OK.
   19. Right-click AutoDiscover, point to New, and then click DWORD Value.
   20. Type ExcludeScpLookup, and then press ENTER.
       
       Note If the ExcludeScpLookup value already exists, go to step u.
   21. Right-click ExcludeScpLookup, and then click Modify.
   22. In the Value data box, type 1, and then click OK.
   23. Right-click AutoDiscover, point to New, and then click DWORD Value.
   24. Type ExcludeSrvRecord, and then press ENTER.
       
       Note If the ExcludeSrvRecord value already exists, go to step y.
   25. Right-click ExcludeSrvRecord, and then click Modify.
   26. In the Value data box, type 1, click OK. Then, close Registry Editor.

To work around this problem, do one of the following:

• Delete the mailboxes on the server that is running Exchange Server 2007 as soon as possible after the data is migrated to Exchange Online.
• Use a different primary SMTP address for the user accounts on Exchange Online and on the on-premise Exchange Server 2007 server.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

The Autodiscover feature uses the primary SMTP address. If an SMTP address conflict occurs, the connection to the on-premise Exchange Server receives priority. For example, an Outlook client will be connected to an on-premise server that is running Exchange Server 2007 if the computer is joined to an on-premise Active Directory domain.

The problem that is described in the "Symptoms" section is most likely to occur during a trial period or during an e-mail coexistence period before user mailboxes are migrated to the Exchange Online environment and before the on-premise mailbox is deleted.