Avoiding Outlook OST regeneration

Hello all-

We are performing an intra-forest domain consolidation (child into parent). Customer is currently on Office 365 which resides on the target. Pre-migration, users would log into their respective child domains and then into the parent for email. 

Our process is to merge their source account into the target. Process is fine and works as advertised.

Some of this customer's remote sites have very slow WAN links (some 1.5-3mb/s) servicing sometime 30-40 people. When the computer is migrated to the parent and Outlook is fired up, the OST is regenerated which clogs the pipe to the point where the business cannot operate.

Research shows this:  https://technet.microsoft.com/en-us/library/cc179067.aspx  Essentially using GPOs to throttle how much traffic will come down.

I think I know the answer to this but is there anyway way to preserve the whole OST post-move? QMMEX is not in play and I don't think a Remote User Collection would be relevant here anyway.

As always, thanks for the assistance.


  • I don't understand why the OST is being recreated in the first place. Assuming you are processing the workstations and the users are using the same user profile, same MAPI profile, the OST should NOT rebuild.
  • In reply to Jeff Shahan:

    We are processing the workstations and the same MAPI profile is being used. OST is definitely being re-generated as you can see the messages being downloaded again.
  • In reply to eric_bergstrom:

    That's odd for sure. Outlook is already connected to the target mailbox so the .OST file shouldn't get recreated. I'm wondering if this has anything to do with the permission behavior of Outlook from your other thread.
  • In reply to Chris.Holley:

    It may. To circumvent the OL and Registry issue, we are pre-processing everything EXCEPT the Registry. Then, when its time to move, process all, move, process Reg again. Now, if I could just get some traction on my Win10 migration issues.....
  • In reply to eric_bergstrom:

    I agree with this. On our last migration, and our current that we are still in testing, the OST must be completely rebuilt. This is evident when you open Outlook to a blank slate and all folders must be updated.
    We are using CPUU to update the addresses for nicks and contacts, as well.
  • In reply to derek.hamaker:

    Derek, this is normal for an Exchange migration. It is common for an AD only migration, intra-forest in this case.