When I use the move-mailbox command will my Outlook clients need to recreate their .OST files?

I’ve had the same question come up a few times recently so thought I'd blog about it as i assumed this is a FAQ.

When migrating from Exchange 2003 to 2007 will Outlook need to regenerate the .OST file?

The short answer is…no, it doesn't need to be created, the move is transparent as far as the user is concerned.

The long-ish answer is…when you use the move-mailbox command the mailbox GUID stays the same across the migration. The Outlook profile is tied to the mailbox GUID, so since the GUID moves with the migration the Outlook profile does not need to be recreated nor does the .OST associated with the profile!


Written by Daniel Kenyon-Smith

Comments (6)
  1. Dan Kenyon-smith says:

    Have you also noticed an increase in the size of the mailbox?

  2. Dan Kenyon-smith says:


    I just need a little bit more info…Do you know what error they are getting in cached mode?  Is the the Outlook Address Book (OAB) working OK? Did you replicate the OAB to E2010 ?  Were any of the e2k3 also DCs ?


  3. Anonymous says:


    I've migrated from Exchange 2003 to 2010. All my clients are Outlook 2003 SP2

    During the coexistence , all was fine

    When I removed / unistaled the last Exchange 2003 servers, All my Outlook clients could not access to an other user folder (shared calendar for example). and they can't access to there own folders permissions (when sharing a calendar for example)

    I've this issue only with cached mode enabled

    When the cached mode is disabled all is OK

    is there a way to fix this issue for all my 500 users

    Thank you in advance

  4. Dan Kenyon-smith says:

    Using the –ConfigurationOnly switch will only move the following attributes:-

    • homeMTA

    • homeMDB

    • msExchHomeServer

    Therefore you’ll still have to recreate the .OST file when using the –ConfigurationOnly

    Note: The –ConfigurationOnly switch is no longer used in Exchange 2010 the command is now –  Set-Mailbox -Database <newdb> -Identity <mailbox Id>

  5. Teo says:

    What about dial-tone.  With 2003, you would have to re-create OST files with dial-tone recovery's.  In Exchange 2007, is the GUID moved when using the -configurationonly switch?

  6. sahil says:

    has any one observed the file size of OST files post migration from Exchange 2003 to Exchange 2010?

    I have seen this in my Lab setup, when I migrate a user, keeping the same outlook client (2007 or 2010) in cache mode, we see OST file size goes up. Is this default behavior?

    Thank You in Advance

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